Methods and apparatus for eyeglass lens curing using ultraviolet light

ABSTRACT

Method and apparatus for making and coating a plastic lens. Oxygen barrier containing photoinitiator is used to cure incompletely cured lens portions. Radiation pulses are used to control lens curing rate. Lens is postcured while in a mold cavity using a conductive heat source.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is a divisional of U.S. patent application Ser. No.08/666,062, filed Jun. 14, 1996, now U.S. Pat. No. 5,928,575, which is adivisional of U.S. patent application Ser. No. 08/636,510, filed Apr.19, 1996 , now U.S. Pat. No. 6,022,498.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates generally to methods and apparatus formaking plastic lenses using ultraviolet light.

2. Description of Related Art

It is conventional in the art to produce optical lenses by thermalcuring techniques from the polymer of diethylene glycolbis(allyl)-carbonate (DEG-BAC). In addition, optical lenses may also bemade using ultraviolet (“UTV”) light curing techniques. See, forexample, U.S. Pat. No. 4,728,469 to Lipscomb et al., U.S. Pat. No.4,879,318 to Lipscomb et al., U.S. Pat. No. 5,364,256 to Lipscomb etal., and U.S. Pat. No. 5,415,816 to Buazza et al., U.S. patentapplication Ser. Nos. 07/021,913 filed Mar. 4, 1987, Ser. No. 07/425,371filed Oct. 26, 1989, Ser. No. 07/931,946 filed Aug. 18, 1992, Ser. No.08/123,886 filed Sep. 20, 1993, Ser. No. 07/932,812 filed Aug. 18, 1992,all of which are hereby specifically incorporated hereby by reference.

Curing of a lens by ultraviolet light tends to present certain problemsthat must be overcome to produce a viable lens. Such problems includeyellowing of the lens, cracking of the lens or mold, optical distortionsin the lens, and premature release of the lens from the mold. Inaddition, many of the useful UV-curable lens forming compositionsexhibit certain characteristics which increase the difficulty of a lenscuring process. For example, due to the relatively rapid nature ofultraviolet light initiated reactions, it is a challenge to provide acomposition which is UV curable to form an eyeglass lens. Excessiveexothermic heat tends to cause defects in the cured lens. To avoid suchdefects, the level of photoinitiator may be reduced to levels below whatis customarily employed in the ultraviolet curing art.

While reducing the level of photoinitiator addresses some problems, itmay also cause others. For instance, lowered levels of photoinitiatormay cause the material in regions near an edge of the lens and proximatea gasket wall in a mold cavity to incompletely cure due to the presenceof oxygen in these regions (oxygen is believed to inhibit curing of manylens forming compositions or materials). Uncured lens formingcomposition tends to result in lenses with “wet” edges covered by stickyuncured lens forming composition. Furthermore, uncured lens formingcomposition may migrate to and contaminate the optical surfaces of thelens upon demolding. The contaminated lens is then often unusable.

Uncured lens forming composition has been addressed by a variety ofmethods (see, e.g., the methods described in U.S. patent applicationSer. No. 07/931,946). Such methods may include removing the gasket andapplying either an oxygen barrier or a photoinitiator enriched liquid tothe exposed edge of the lens, and then re-irradiating the lens with adosage of ultraviolet light sufficient to completely dry the edge of thelens prior to demolding. During such irradiation, however, higher thandesirable levels of irradiation, or longer than desirable periods ofirradiation, may be required. The additional ultraviolet irradiation mayin some circumstances cause defects such as yellowing in the lens.

The low photoinitiator levels utilized in many ultraviolet curable lensforming compositions may produce a lens which, while fully-cured asmeasured by percentage of remaining double bonds, may not possesssufficient crosslink density on the lens surface to provide desirabledye absorption characteristics during the tinting process.

Various methods of increasing the surface density of such UV curablelenses are described in U.S. patent application Ser. No. 07/931,946. Inone method, the lens is demolded and then the surfaces of the lens areexposed directly to ultraviolet light. The relatively short wavelengths(around 254 nm) provided by some UV sources (e.g., a mercury vapor lamp)tend to cause the material to crosslink quite rapidly. An undesirableeffect of this method, however, is that the lens tends to yellow as aresult of such exposure.

Another method involves exposing the lens to relatively shortwavelengths while it is still within a mold cavity formed between glassmolds. The glass molds tend to absorb the more effective shortwavelengths, while transmitting wavelengths of about 365 nm. This methodgenerally requires long exposure times and often the infrared radiationabsorbed by the lens mold assembly will cause premature release of thelens from a mold member. The lens mold assembly may be heated prior toexposure to high intensity ultraviolet light, thereby reducing theamount of radiation necessary to attain a desired level of crosslinkdensity. This method, however, is also associated with a higher rate ofpremature release.

It is well known in the art that a lens mold/gasket assembly may beheated to cure the lens forming composition from a liquid monomer to asolid polymer. It is also well known that such a lens may be thermallypostcured by applying convective heat to the lens after the molds andgaskets have been removed from the lens.

In this application the terms “lens forming material” and “lens formingcompositions” are used interchangeably.

SUMMARY OF THE INVENTION

One aspect of the invention relates to applying an oxygen barrier aroundthe exposed edges of a lens to initiate the reaction of incompletelycured lens forming material proximate the lens edges. In an embodiment,a liquid polymerizable lens forming composition is placed in a moldcavity having at least two molds and/or a gasket. Ultraviolet rays maybe directed toward at least one of the mold members to substantiallycure the lens forming composition to a lens having material proximatethe edges of the lens that is not fully cured. The gasket may be removedto expose the edges of the lens, and an oxygen barrier comprising aphotoinitiator may be placed around the exposed edges of the lens suchthat at least a portion of the oxygen barrier photoinitiator isproximate lens forming composition that is not fully cured. A portion ofthe incompletely cured material may be removed manually prior to theapplication of the oxygen barrier. Subsequently another set ofultraviolet rays may be directed towards the lens such that at least aportion of the oxygen barrier photoinitiator initiates reaction of lensforming composition while the oxygen barrier substantially preventsoxygen from outside the oxygen barrier from contacting at least aportion of the lens forming composition. The lens may be allowed to cooland the oxygen barrier may be removed. The lens may be tinted after thecure is completed.

The oxygen barrier may include a flexible, stretchable, self-sealingfilm that is at least partially transparent to ultraviolet rays. Theoxygen barrier may include polyethylene impregnated with aphotoinitiator. The film may include a strip of high densitypolyethylene that is about 0.01-1.0 mm thick, and more preferably about0.01-0.10 mm thick. Thicker films tend to be less conformable andstretchable. The oxygen barrier may include a plastic film that is lessthan about 0.025 mm thick. (e.g., about 0.0127 mm thick) and that wasmade by (a) immersing or running a plastic film in or through a solutioncomprising a photoinitiator and an etching agent (b) removing theplastic film from the solution, and (c) drying the plastic film. Asurface on the plastic film may be chemically etched prior to or whileimmersing the plastic film in the solution.

Another aspect of the invention relates to applying conductive heat tothe face of a lens. In an embodiment of the invention, a liquidpolymerizable lens forming composition is placed in a mold cavity havinga first mold member and a second mold member. First ultraviolet rays maybe directed toward at least one of the mold members to cure the lensforming composition to a lens. A mold member may be applied to asubstantially solid conductive heat source. Heat may be conductivelyapplied to a face of the lens by (a) conductively transferring heat to aface of a mold member from the conductive heat source, and (b)conductively transferring heat through such mold member to the face ofthe lens.

In an embodiment, a flexible heat distributor may be placed between theheat source and the mold member to partially insulate the mold memberand to slowly and uniformly transfer heat to the face of the moldmember. The distributor may be shaped to conform to the face of a moldmember. The heat source may include a concave element that may conformto the convex face of a mold member. The heat source may include aconvex element that may conform to the concave face of a mold member.The temperature of the heat source may be thermostatically controlled.Heat may be conductively applied through a mold member to the back faceof the lens, thereby enhancing the cross-linking and tintability of thelens forming material proximate to the surface of the back face of thelens (e.g., when an untintable scratch resistant coating is on the frontface of the lens).

In an embodiment of the invention an eyeglass lens may be formed by (a)placing a liquid, polymerizable lens-forming composition in a moldcavity defined by at least a first mold member and a second mold member,(b) applying a plurality of preferably high intensity ultraviolet lightpulses to the lens forming composition, at least one of the pulseshaving a duration of less than about one second (more preferably lessthan about 0.1 seconds, and more preferably between 0.1 and 0.001seconds), and (c) curing the lens forming composition to form asubstantially clear eyeglass lens in a time period of less than 30minutes (more preferably less than 20 minutes, and more preferably stillless than 15 minutes).

The pulses preferably have a sufficiently high intensity such thatreaction is initiated in substantially all of the lens formingcomposition that is exposed to pulses in the mold cavity. In oneembodiment reaction is initiated in substantially all of any crosssection of the lens forming composition that is exposed to pulses in themold cavity. Preferably the temperature begins to rise after suchapplication of UV light.

The lens forming composition may be exposed to UV light from one, two,or multiple sources. Two sources may be applied on opposite sides of themold cavity to apply light to the lens forming composition from twosides. In an alternate embodiment the lens forming composition isexposed to a relatively low intensity ultraviolet light while the pulsesare applied. Such pulses are preferably relatively high in intensity,and are preferably applied to the other side of the mold cavity than therelatively low intensity light.

The lens forming composition is preferably exposed to a relatively lowintensity ultraviolet light while the pulses are applied, the relativelylow intensity light having an intensity of less than 0.01 watt/ cm² (andmore preferably less than 0.001 watt/ cm², and more preferably still2-30 milliwatts/ cm2), as measured on an outside surface of a moldmember of the mold cavity. The relatively low intensity light tends toprovide a low amount of light to keep the reaction going in a moresteady or even manner between pulses.

Preferably at least one or even all of the pulses has an intensity of atleast 0.01 watt/ cm², as measured on an outside surface of a mold memberof the mold cavity. Alternately at least one or even all of the pulseshave an intensity of at least 0.1 or 1 watt/ cm².

Sufficient ultraviolet light can be applied such that the temperature ofthe lens forming composition begins to increase. Then preferably atleast 5 minutes of waiting or darkness occurs before applying additionallight (e.g., pulses). The waiting or darkness allows heat to dissipate,thus tending to prevent excessive heat buildup in the mold cavity. Inone embodiment at least 5, 10, or 20 pulses are applied to the lensforming composition before waiting for about 5-8 minutes and thenadditional light is applied.

The eyeglass lens has an average thickness of at least about 1.5-2.0 mm.Thicker lenses tend to be more difficult to cure with continuousnon-pulsed light.

The mold cavity is preferably cooled with air or cooled air. Onesignificant advantage of light pulses is that ambient air may be used tocool the mold cavity, instead of cooled air. Thus significant lenscuring costs may be avoided since air coolers tend to be costly topurchase and operate.

The pulses preferably emanate from a flash source of light (i.e., “aflash light”) such as a xenon light source. Preferably pulses areapplied such that the lens forming composition is oversaturated withultraviolet light during at least one pulse. Flash lights areadvantageous in that they have a short “warm-up” time (as opposed tocontinuous lights that tend to require 5-60 minutes to stabilize).

Lenses that are more difficult to cast, such as lenses with a powergreater than positive 2 diopters or lenses with a power less than minus4 diopters, may be formed with pulsed light.

One advantage of pulsed light application via flash lights is that eventhough higher intensities of light are applied, because the duration ofthe pulses is so short the total amount of light energy applied to curethe lens forming composition is lessened. Thus less radiant heat isapplied to the mold cavity, thereby reducing cooling requirements.Moreover, energy is saved. In one embodiment less than 20, 10, 5, or 1Joule/ cm² of energy is applied to cure the lens forming compositioninto a lens.

Preferably the ultraviolet light is applied as a function of thetemperature of the lens forming composition, as measured directly orindirectly by measuring a temperature within the chamber (e.g., atemperature of at least a portion of the mold cavity) or by measuring atemperature of air in or exiting the chamber.

In another embodiment of the invention, an eyeglass lens may be cured by(a) placing a liquid, polymerizable lens forming composition in a moldcavity defined by at least a first mold member and a second mold member,the lens forming composition comprising a photoinitiator, (b) applyingultraviolet light at an intensity to the lens forming compositionthrough at least one of the mold members for a selected period of timesuch that a temperature of the composition begins to increase, (c)decreasing the intensity of the ultraviolet light to inhibit thetemperature of the lens forming composition from increasing to aselected first temperature, (d) allowing an exothermic reaction of thelens forming composition to increase the temperature of the lens formingcomposition to a second temperature, the second temperature being lessthan the selected first temperature, (e) curing the lens formingcomposition to form a substantially clear eyeglass lens by: (i) applyingultraviolet light at an intensity to the lens forming compositionthrough at least one of the mold members, and (ii) decreasing theintensity of the ultraviolet light; and (f) wherein the eyeglass lens isformed from the lens forming composition in a time period of less thanabout 30 minutes.

In another embodiment of the invention an eyeglass lens may be made by(a) placing a liquid, polymerizable lens-forming composition in a moldcavity defined by at least a first mold member and a second mold member,the lens forming composition comprising a photoinitiator, (b) applyingfirst ultraviolet light to at least one of the mold members for aselected first period of time such that a temperature of the lensforming composition begins to increase, (c) removing the firstultraviolet light from at least one of the mold members, therebyinhibiting the temperature of the composition from increasing to aselected first temperature, and (d) repeatedly and alternatelyperforming the following steps to complete the formation of a lens: (i)applying second ultraviolet light to at least one of the mold membersfor a selected second period of time and (ii) removing the secondultraviolet light from at least one of the mold members for a selectedthird period of time.

In an alternate embodiment of the invention an eyeglass lens may be madeby (a) placing a liquid, polymerizable lens forming composition in amold cavity defined by at least a first mold member and a second moldmember, the lens forming composition comprising a photoinitiator, (b)directing ultraviolet light at a first intensity toward at least one ofthe mold members for a selected first period of time such that atemperature of the composition begins to increase, (c) decreasing thefirst intensity of ultraviolet light from at least one of the moldmembers, and (d) repeatedly directing a plurality of pulses ofultraviolet to the lens forming composition through at least one of themold members to complete formation of a substantially clear eyeglasslens, at least one of the pulses lasting for a second period of time,and wherein a third period of time exists between application of atleast two of the pulses.

An apparatus of the invention may include: (a) a first mold memberhaving a casting face and a non-casting face, (b) a second mold memberhaving a casting face and a non-casting face, the second mold memberbeing spaced apart from the first mold member during use such that thecasting faces of the first mold member and the second mold member atleast partially define a mold cavity, (c) a first pulse light generatoradapted to generate and direct a pulse of ultraviolet light toward atleast one of the first and second mold members during use, and (d) acontroller adapted to control the first pulse light generator such thatultraviolet light is directed in a plurality of pulses toward at leastone of the first and second mold members, at least one of the pulseshaving a duration of less than one second.

A system of the invention may include (a) a lens forming compositioncomprising a photoinitiator, (b) a first mold member having a castingface and a non-casting face, (c) a second mold member having a castingface and a non-casting face, the second mold member being spaced apartfrom the first mold member during use such that the casting faces of thefirst mold member and the second mold member at least partially define amold cavity for the lens forming composition, (d) a first pulse lightgenerator adapted to generate and direct a pulse of ultraviolet lighttoward at least one of the first and second mold members during use, (e)a controller adapted to control the first pulse light generator suchthat ultraviolet light is directed in a plurality of pulses toward atleast one of the first and second mold members, at least one of thepulses having a duration of less than one second, and (f) wherein thesystem is adapted to cure the lens forming composition to form asubstantially clear eyeglass lens in less than 30 minutes.

The lens forming composition preferably comprises at least onepolyethylenic-functional monomer containing at least two ethylenicallyunsaturated groups selected from acrylyl and methacrylyl, at least onepolyethylenic-functional monomer containing at least three ethylenicallyunsaturated groups selected from acrylyl and methacrylyl, and/or anaromatic containing bis(allyl carbonate)-functional monomer.

A system of the invention may also include: (a) a lens formingcomposition comprising a photoinitiator, (b) a mold cavity chambercomprising a first mold member having a casting face and a non-castingface, a second mold member having a casting face and a non-casting face,the second mold member being spaced apart from the first mold memberduring use such that the casting faces of the first mold member and thesecond mold member at least partially define a mold cavity for the lensforming composition, (c) a first light generator adapted to generate anddirect an ultraviolet light in a first intensity toward at least one ofthe first and second mold members during use, (d) a temperature sensoradapted to sense a temperature in the chamber or a temperature of airexiting the chamber, (e) a controller coupled to the temperature sensorand adapted to control the first light generator such that the firstintensity of ultraviolet light directed toward at least one of the firstand second mold members is decreased when a temperature measured by thetemperature sensor substantially increases, and (f) wherein the systemis adapted to cure the lens forming composition to form a substantiallyclear eyeglass lens in less than 30 minutes.

An apparatus of the invention may include a light sensor adapted tomeasure the intensity of light directed by the ultraviolet lightgenerator, and a filter adapted to inhibit light other than ultravioletlight from impinging upon the light sensor.

BRIEF DESCRIPTION OF THE DRAWINGS

The above brief description as well as further objects, features andadvantages of the methods and apparatus of the present invention will bemore fully appreciated by reference to the following detaileddescription of presently preferred but nonetheless illustrativeembodiments in accordance with the present invention when taken inconjunction with the accompanying drawings in which:

FIG. 1 is a perspective view of an apparatus for producing a plasticlens.

FIG. 2 is a cross-sectional view of the apparatus taken along line 2—2of FIG. 1.

FIG. 3 is a cross-sectional view of the apparatus taken along line 3—3of FIG. 2.

FIG. 4 is a detail view of a component of the apparatus.

FIG. 5 is a detail view of a component of the apparatus.

FIG. 6 is a cross-sectional view of a lens cell for use in an apparatusof the invention.

FIG. 7 is a view of an embodiment of a shutter system.

FIGS. 8(a) and 8(b) are respectively is a top and side view of anembodiment of a heat distributor to be placed between a heat source anda mold surface.

FIG. 9 is a schematic block diagram of an alternate process and systemfor making and postcuring a plastic lens.

FIG. 10 is a schematic diagram of an apparatus to apply UV light to alens or mold assembly.

FIG. 11 is a view of an embodiment of a lens.

FIG. 12 is a view of an embodiment of an oxygen barrier withphotoinitiator.

FIG. 13 is a schematic diagram of a lens curing apparatus with a lightsensor and controller.

FIG. 14 is a schematic view of the front of a lens curing apparatus.

FIG. 15 is a schematic view of the side of a lens curing apparatus.

FIG. 16 is a view of an embodiment of a heat source and a heatdistributor.

FIG. 17 is a view of various embodiments of a heat source and heatdistributors.

FIG. 18 is a view of an embodiment of a heat source and a heatdistributor.

FIG. 19 is a view of an embodiment of two mold members and a gasket.

FIG. 20 is a graph illustrating a temperature profile of a continuousradiation cycle.

FIG. 21 is a graph illustrating temperature profiles for a continuousirradiation cycle and a pulse irradiation cycle employed with amold/gasket set having a 3.00 D base curve, and while applying cooledair at 58° F. to the mold/gasket set.

FIG. 22 is a chart illustrating qualitative relationships among curingcycle variables.

FIG. 23 is a graph illustrating temperature profiles for one curingcycle for a mold/gasket set having a 6.00 D base curve and used withthree different light levels.

FIG. 24 is a graph illustrating continuous and pulsed temperatureprofiles for a curing cycle employing a mold/gasket set with a 6.00 Dbase curve.

FIG. 25 is a graph illustrating continuous and pulsed temperatureprofiles for a curing cycle employing a mold/gasket set with a 4.50 Dbase curve.

FIG. 26 is a graph illustrating continuous and pulsed temperatureprofiles for a curing cycle employing a mold/gasket set with a 3.00 Dbase curve.

FIG. 27 is a view of an embodiment of a system simultaneously employingboth a flash light source and a continuous UV (e.g., fluorescent)source.

FIG. 28 is an embodiment of a system simultaneously employing two flashlight sources.

FIG. 29 is an embodiment of a system employing an ultraviolet lightcontroller.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

Apparatus, operating procedures, equipment, systems, methods, andcompositions for lens curing using ultraviolet light are available fromRapid Cast, Inc., Q2100, Inc., and Fast Cast, Inc. in East Rockaway,N.Y. and Louisville, Ky. The Fast Cast, Inc. publication entitled“Operation Manual For The FastCast LenSystem” is hereby incorporated byreference.

Referring now to FIG. 1, a plastic lens curing chamber of the presentinvention is generally indicated by reference numeral 10. The lenscuring chamber 10 preferably communicates through a plurality of pipes12 with an air source (not shown), the purpose of which will bediscussed below.

As shown in FIG. 2, the plastic lens curing chamber 10 may include anupper lamp chamber 14, an irradiation chamber 16, and a lower lampchamber 18. The upper lamp chamber 14 may be separated from theirradiation chamber 16 by a plate 20. The lower lamp chamber may beseparated from the irradiation chamber 16 by a plate 22. The upper lampchamber 14, the irradiation chamber 16, and the lower lamp chamber 18may be isolated from ambient air by upper lamp chamber doors 24,irradiation chamber doors 26, and lower lamp chamber doors 28,respectively. While the upper lamp chamber doors 24, the irradiationchamber doors 26 and the lower lamp chamber doors 28 are shown in FIG. 1as including two corresponding door members, those of ordinary skill inthe art will recognize that the doors 24, 26 and 28 may include singleor multiple door members. The upper lamp chamber doors 24, theirradiation chamber doors 26 and the lower lamp chamber doors 28 may beslidingly mounted in guides 30. As shown in FIG. 2, vents 32 maycommunicate with upper lamp chamber 14 and lower lamp chamber 18 by wayof corresponding vent chambers 34 and openings 36 disposed in plate 20and plate 22. Each vent 32 may be shielded by a vent cover 38.

As shown in FIG. 3, vents 33 may be disposed in the irradiation chamberdoors 26 and communicate with irradiation chamber 16. Each vent 33 maybe shielded by a vent cover 35.

As shown in FIGS. 2 and 3, a plurality of light generating devices orlamps 40 may be disposed within each of upper lamp chamber 14 and lowerlamp chamber 18. Preferably, upper lamp chamber 14 and lower lampchamber 18 each include three lamps 40 that are arranged in a triangularfashion in which the lamps 40 in the upper lamp chamber 14 are disposedwith the point of the triangle pointing upwards whereas the lamps 40 inthe lower lamp chamber 18 are disposed with the point of the trianglepointing downward. The lamps 40, preferably, generate ultraviolet lighthaving a wavelength in the range of at least approximately 300 nm to 400nm since the effective wavelength spectrum for curing the lens formingmaterial lies in the 300 nm to 400 nm region. The lamps 40 may besupported by and electrically connected to suitable fixtures 42.

An exhaust fan 44 may communicate with upper lamp chamber 14 while anexhaust fan 46 may communicate with lower lamp chamber 18.

As noted above, the upper lamp chamber 14 may be separated from theirradiation chamber 16 by plate 20. Similarly, lower lamp chamber 18 maybe separated from the irradiation chamber 16 by plate 22. The plates 20and 22 may include apertures 48 and 50, respectively, through which thelight generated by lamps 40 may be directed so as to impinge upon a lenscell 52 (shown in phantom in FIG. 2). The diameter of the lens cell 52is preferably approximately 74 mm. The apertures 48 and 50 preferablyrange from about 70 mm to about 140 mm.

In one embodiment an upper light filter 54 rests upon plate 20 while alower light filter 56 rests upon plate 22 or is supported by brackets57. The upper light filter 54 and lower light filter 56 are shown inFIG. 2 as being made of a single filter member, however, those ofordinary skill in the art will recognize that each of the upper lightfilter 54 and lower light filter 56 may include two or more filtermembers. The components of upper light filter 54 and lower light filter56 preferably are modified depending upon the characteristics of thelens to be molded. For instance, in a preferred embodiment for makingnegative lenses, the upper light filter 54 includes a plate of Pyrexglass that is frosted on both sides resting upon a plate of clear Pyrexglass. The lower light filter 56 includes a plate of Pyrex glass frostedon one side resting upon a plate of clear Pyrex glass with a device forreducing the intensity of ultraviolet light incident upon the centerportion in relation to the edge portion of the lens being disposedbetween the plate of frosted Pyrex and the plate of clear Pyrex glass.

Conversely, in a preferred arrangement for producing positive lenses,the upper light filter 54 includes a plate of Pyrex glass frosted on oneor both sides and a plate of clear Pyrex glass resting upon the plate offrosted Pyrex glass with a device for reducing the intensity ofultraviolet light incident upon the edge portion in relation to thecenter portion of the lens being disposed between the plate of clearPyrex glass and the plate of frosted Pyrex glass. The lower light filter56 includes a plate of clear Pyrex glass frosted on one side restingupon a plate of clear Pyrex glass with a device for reducing theintensity of ultraviolet light incident upon the edge portion inrelation to the center portion of the lens being disposed between theplates of clear Pyrex glass. In this arrangement, in place of a devicefor reducing the relative intensity of ultraviolet light incident uponthe edge portion of the lens, the diameter of the aperture 50 can bereduced to achieve the same result, i.e. to reduce the relativeintensity of ultraviolet light incident upon the edge portion of thelens.

It will be apparent to those skilled in the art that each filter 54 or56 could be composed of a plurality of filter members or include anyother means or device effective to reduce the light to its desiredintensity, to diffuse the light and/or to create a light intensitygradient across the lens cell 52. Alternately, in certain embodiments nofilter elements may be used.

Preferably, the upper light filter 54 or the lower light filter 56 eachinclude at least one plate of Pyrex glass having at least one frostedsurface. Also, either or both of the upper light filter 54 and the lowerlight filter 56 may include more than one plate of Pyrex glass eachfrosted on one or both surfaces, and/or one or more sheets of tracingpaper. After passing through frosted Pyrex glass, the ultraviolet lightis believed to have no sharp intensity discontinuities which is believedto lead to a reduction in optical distortions in the finished lens insome instances. Those of ordinary skill in the art will recognize thatother means may be used to diffuse the ultraviolet light so that it hasno sharp intensity discontinuities.

Preferably disposed within the irradiation chamber 16 are a left stage58, a center stage 60, and a right stage 62, each of which preferablyincludes a plurality of steps 64. The left stage 58 and center stage 60define a left irradiation chamber 66 while the right stage 62 and centerstage 60 define a right irradiation chamber 68. A cell holder 70, shownin phantom in FIG. 2 and in detail in FIG. 4, may be disposed withineach of left irradiation chamber 66 and right irradiation chamber 68.The cell holder 70 may include a peripheral step 72 that is designed toallow a cell holder 70 to be supported upon complementary steps 64 ofleft stage 58 and center stage 60, and center stage 60 and right stage62, respectively. As shown in FIG. 4, each cell holder 70 also mayinclude a central bore 74 to allow the passage therethrough ofultraviolet light from the lamps 40 and an annular step 76 which isdesigned to support a lens cell 52 in a manner described below.

As shown in FIG. 6, each lens cell 52 may include opposed mold members78, separated by an annular gasket 80 to define a lens molding cavity82. The opposed mold members 78 and the annular gasket 80 may be shapedand selected in a manner to produce a lens having a desired diopter.

The mold members 78 are preferably formed of any suitable material thatwill permit rays of ultraviolet light to pass therethrough. The moldmembers 78 are preferably formed of glass. Each mold member 78 has anouter peripheral surface 84 and a pair of opposed surfaces 86 and 88with the surfaces 86 and 88 being precision ground. Preferably the moldmembers 78 have desirable ultraviolet light transmission characteristicsand both the casting surface 86 and non-casting surface 88 preferablyhave no surface aberrations, waves, scratches or other defects as thesemay be reproduced in the finished lens.

As noted above, the mold members 78 are adapted to be held in spacedapart relation to define a lens molding cavity 82 between the facingsurfaces 86 thereof. The mold members 78 are preferably held in a spacedapart relation by a T-shaped flexible annular gasket 80 that seals thelens molding cavity 82 from the exterior of the mold members 78. In use,the gasket 80 may be supported on the annular step 76 of the cell holder70.

In this manner, the upper or back mold member 90 has a convex innersurface 86 while the lower or front mold member 92 has a concave innersurface 86 so that the resulting lens molding cavity 82 is shaped toform a lens with a desired configuration. Thus, by selecting the moldmembers 78 with a desired surface 86, lenses with differentcharacteristics, such as focal lengths, may be made by the apparatus 10.

Rays of ultraviolet light emanating from lamps 40 pass through the moldmembers 78 and act on a lens forming material disposed in the moldcavity 82 in a manner discussed below so as to form a lens. As notedabove, the rays of ultraviolet light may pass through a suitable filter54 or 56 to impinge upon the lens cell 52.

The mold members 78, preferably, are formed from a material that willnot allow ultraviolet radiation having a wavelength below approximately300 nm to pass therethrough. Suitable materials are Schott Crown, S-1 orS-3 glass manufactured and sold by Schott Optical Glass Inc., of Duryea,Pa. or Coming 8092 glass sold by Coming Glass of Corning, N.Y. A sourceof molds may be Opticas Devlyn S.A. (Mexico City, Mexico) and/or TitmusInc. (Fredricksburg, Va.).

The annular gasket 80 may be formed of vinyl material that exhibits goodlip finish and maintains sufficient flexibility at conditions throughoutthe lens curing process. In a preferred embodiment, the annular gasket80 is formed of silicone rubber material such as GE SE6035 which iscommercially available from General Electric. In another preferredembodiment, the annular gasket 80 is formed of copolymers of ethyleneand vinyl acetate which are commercially available from E. I. DuPont deNemours & Co. under the trade name ELVAX7. Preferred ELVAX7 resins areELVAX7 350 having a melt index of 17.3-20.9 dg/min and a vinyl acetatecontent of 24.3-25.7 wt. %, ELVAX7 250 having a melt index of 22.0-28.0dg/min and a vinyl acetate content of 27.2-28.8 wt. %, ELVAX7 240 havinga melt index of 38.0-48.0 dg/min and a vinyl acetate content of27.2-28.8 wt. %, and ELVAX7 150 having a melt index of 38.0-48.0 dg/minand a vinyl acetate content of 32.0-34.0 wt. %. Regardless of theparticular material, the gaskets 80 may be prepared by conventionalinjection molding or compression molding techniques which are well-knownby those of ordinary skill in the art.

As shown in phantom in FIG. 2, in section in FIG. 3, and in detail inFIG. 5, an upper and lower air distribution device 94 is disposed ineach of left irradiation chamber 66 and right irradiation chamber 68.Each air distribution device 94 is connected to a pipe 12. As shown inFIG. 5, each air distribution device 94 includes a plenum portion 95 anda substantially cylindrical opening 96 having orifices 98 disposedtherein to allow for the expulsion of air from the air distributiondevice 94. The diameter of the orifices 98 may be constant, or may varyaround the circumference of cylindrical opening 96 preferably reaching amaximum when directly opposite the plenum portion 95 of air distributiondevice 94 and preferably reaching a minimum immediately adjacent theplenum portion 95. In addition, the orifices 98 are designed to blow airtoward a lens cell 52 that may be disposed in a lens cell holder 70 andinstalled in left irradiation chamber 66 or right irradiation chamber68.

In operation, the apparatus of the present invention may beappropriately configured for the production of positive lenses which arerelatively thick at the center or negative lenses which are relativelythick at the edge. To reduce the likelihood of premature release, therelatively thick portions of a lens preferably are polymerized at afaster rate than the relatively thin portions of a lens.

The rate of polymerization taking place at various portions of a lensmay be controlled by varying the relative intensity of ultraviolet lightincident upon particular portions of a lens. The rate of polymerizationtaking place at various portions of a lens may also be controlled bydirecting air across the mold members 78 to cool the lens cell 52.

For positive lenses the intensity of incident ultraviolet light ispreferably reduced at the edge portion of the lens so that the thickercenter portion of the lens polymerizes faster than the thinner edgeportion of the lens. Conversely, for a negative lens, the intensity ofincident ultraviolet light is preferably reduced at the center portionof the lens so that the thicker edge portion of the lens polymerizesfaster than the thinner center portion of the lens. For either apositive lens or a negative lens, air may be directed across the facesof the mold members 78 to cool the lens cell 52. As the overallintensity of incident ultraviolet light is increased, more cooling isneeded which can be accomplished by either or both of increasing thevelocity of the air and reducing the temperature of the air.

It is well known by those of ordinary skill in the art that lens formingmaterials having utility in the present invention tend to shrink as theycure. If the relatively thin portion of a lens is allowed to polymerizebefore the relatively thick portion, the relatively thin portion willtend to be rigid at the time the relatively thick portion cures andshrinks and the lens will either release prematurely from or crack themold members 78. Accordingly, when the relative intensity of ultravioletlight incident upon the edge portion of a positive lens is reducedrelative to the center portion, the center portion polymerizes fasterand shrinks before the edge portion is rigid so that the shrinkage ismore uniform. Conversely, when the relative intensity of ultravioletlight incident upon the center portion of a negative lens is reducedrelative to the edge portion, the edge portion polymerizes faster andshrinks before the center becomes rigid so that the shrinkage is moreuniform.

The variation of the relative intensity of ultraviolet light incidentupon a lens may be accomplished in a variety of ways. According to onemethod, in the case of a positive lens, a ring of opaque material may beplaced between the lamps 40 and the lens cell 52 so that the incidentultraviolet light falls mainly on the thicker center portion of thelens. Conversely, for a negative lens, a disk of opaque material may beplaced between the lamps 40 and the lens cell 52 so that the incidentultraviolet light falls mainly on the edge portion of the lens.

According to another method, in the case of a negative lens, a sheetmaterial having a variable degree of opacity ranging from opaque at acentral portion to transparent at a radial outer portion is disposedbetween the lamps 40 and the lens cell 52. Conversely, for a positivelens, a sheet material having a variable degree of opacity ranging fromtransparent at a central portion to opaque at a radial outer portion isdisposed between the lamps 40 and the lens cell 52.

Those of ordinary skill in the art will recognize that there are a widevariety of techniques other than those enumerated above for varying theintensity of the ultraviolet light incident upon the opposed moldmembers 78.

In some embodiments, the intensity of the incident light has beenmeasured and determined to be approximately 3.0 to 5.0 milliwatts persquare centimeter (mW/cm²) prior to passing through either the upperlight filter 54 or the lower light filter 56 and the total intensity atthe thickest part of the lens ranges from 0.6 to 2.0 mW/cm² while theintensity at the thinnest portion of the lens ranges from 0.1 to 1.5mW/cm². In some embodiments the overall light intensity incident on thelens cell 52 has less of an impact on the final product than therelative light intensity incident upon the thick or thin portions of thelens so long as the lens cell 52 is sufficiently cooled to reduce thepolymerization rate to an acceptable level.

It has been determined that in some embodiments the finished power of anultraviolet light polymerized lens may be controlled by manipulating thedistribution of the incident ultraviolet light striking the opposed moldmembers 78. For instance, for an identical combination of mold members78 and gasket 80, the focusing power of the produced lens may beincreased or decreased by changing the pattern of intensity ofultraviolet light across the lens mold cavity 82 or the faces of theopposed mold members 78.

As the lens forming material begins to cure, it passes through a gelstate, the pattern of which within the lens cell 52 leads to the properdistribution of internal stresses generated later in the cure when thelens forming material begins to shrink.

As the lens forming material shrinks during the cure, the opposed moldmembers 78 will preferably flex as a result of the different amounts ofshrinkage between the relatively thick and the relatively thin portionsof the lens. When a negative lens, for example, is cured, the upper orback mold member 90 will preferably flatten and the lower or front moldmember 92 will preferably steepen with most of the flexing occurring inthe lower or front mold member 92. Conversely, with a positive lens, theupper or back mold member 90 will preferably steepen and the lower orfront mold member 92 will preferably flatten with most of the flexingoccurring in the upper or back mold member 90.

By varying the intensity of the ultraviolet light between the relativelythin and the relatively thick portions of the lens in the lens formingcavity 82, it is possible to create more or less total flexing. Thoselight conditions which result in less flexing will tend to minimize thepossibility of premature release.

The initial curvature of the opposed mold members 78 and the centerthickness of the lens produced can be used to compute the theoretical orpredicted power of the lens. The ultraviolet light conditions can bemanipulated to alter the power of the lens to be more or less thanpredicted. The greater the diameter of the disk of opaque material, themore negative (−) power the resultant lens will tend to exhibit.

When the lenses cured by the ultraviolet light are removed from theopposed mold members 78, they are typically under a stressed condition.It has been determined that the power of the lens can be brought to afinal resting power, by subjecting the lenses to a post-curing heattreatment to relieve the internal stresses developed during the cure andcause the curvature of the front and the back of the lens to shift.Typically, the lenses are cured by the ultraviolet light in about 10-30minutes (preferably about 15 minutes). The post-curing heat treatment isconducted at approximately 85-120° C. for approximately 5-15 minutes.Preferably, the post-curing heat treatment is conducted at 100-110° C.for approximately 10 minutes. Prior to the post-cure, the lensesgenerally have a lower power than the final resting power. Thepost-curing heat treatment reduces yellowing of the lens and reducesstress in the lens to alter the power thereof to a final power. Thepost-curing heat treatment can be conducted in a conventional convectionoven or any other suitable device.

In addition, as described below, in certain embodiments heat may beconductively applied to the molds and/or lens, thereby enhancing thequality of the cured lenses.

The ultraviolet lamps 40 preferably are maintained at a temperature atwhich the lamps 40 1o deliver maximum output. The lamps 40, preferably,are cooled because the intensity of the light produced by the lamps 40fluctuates when the lamps 40 are allowed to overheat. In the apparatusdepicted in FIG. 2, the cooling of the lamps 40 is accomplished bysucking ambient air into the upper lamp chamber 14 and lower lampchamber 18 through vent 32, vent chambers 34 and openings 36 by means ofexhaust fans 44 and 46, respectively. Excessive cooling of the lamps 40should be avoided, however, as the intensity of the light produced bythe lamps 40 is reduced when the lamps 40 are cooled to an excessivedegree.

As noted above, the lens cell 52 is preferably cooled during curing ofthe lens forming material as the overall intensity of the incidentultraviolet light is increased. Cooling of the lens cell 52 generallyreduces the likelihood of premature release by slowing the reaction andimproving adhesion. There are also improvements in the optical quality,stress characteristics and impact resistance of the lens. Cooling of thelens cell 52 is preferably accomplished by blowing air across the lenscell 52. The air preferably has a temperature ranging between 15 and 85°F. (about −9.4° C. to 29.4° C.) to allow for a curing time of between 30and 10 minutes. The air distribution devices 94 depicted in FIG. 5 havebeen found to be particularly advantageous as they are specificallydesigned to direct air directly across the surface of the opposed moldmembers 78. After passing across the surface of the opposed mold members78, the air emanating from the air distribution devices 94 is ventedthrough vents 33. Alternately the air emanating from the airdistribution devices 94 may be recycled back to an air cooler.

The lens cell 52 may also be cooled by disposing the lens cell in aliquid cooling bath.

The opposed mold members 78 are preferably thoroughly cleaned betweeneach curing s run as any dirt or other impurity on the mold members 78may cause premature release. The mold members 78 are cleaned by anyconventional means well known to those of ordinary skill in the art suchas with a domestic cleaning product, i.e., Mr. Clean™ available fromProctor and Gamble. Those of ordinary skill in the art will recognize,however, that many other techniques may also be used for cleaning themold members 78.

Yellowing of the finished lens may be related to the monomercomposition, the identity of the photoinitiator, and the concentrationof the photoinitiator.

When casting a lens, particularly a positive lens that is thick in thecenter, cracking may be a problem. Addition polymerization reactions,including photochemical addition polymerization reactions, areexothermic. During the process, a large temperature gradient may buildup and the resulting stress may cause the lens to crack.

The formation of optical distortions usually occurs during the earlystages of the polymerization reaction during the transformation of thelens forming composition from the liquid to the gel state. Once patternsleading to optical distortions form they are difficult to eliminate.When gelation occurs there typically is a rapid temperature rise. Theexothermic polymerization step causes a temperature increase, which inturn causes an increase in the rate of polymerization, which causes afurther increase in temperature. If the heat exchange with thesurroundings is not sufficient enough there will be a runaway situationthat leads to premature release, the appearance of thermally causedstriations and even breakage.

Accordingly, when continuous UV light is applied, it is preferred thatthe reaction process be smooth and not too fast but not too slow. Heatis preferably not generated by the process so fast that it cannot beexchanged with the surroundings. The incident ultraviolet lightintensity preferably is adjusted to allow the reaction to proceed at adesired rate. It is also preferred that the seal between the annulargasket 80 and the opposed mold members 78 be as complete as possible.

Factors that have been found to lead to the production of lenses thatare free from optical distortions are (1) achieving a good seal betweenthe annular gasket 80 and the opposed mold members 78; (2) using moldmembers 78 having surfaces that are free from defects; (3) using aformulation having an appropriate type and concentration ofphotoinitiator that will produce a reasonable rate of temperature rise;and (4) using a homogeneous formulation. Preferably, these conditionsare optimized.

Premature release of the lens from the mold will result in anincompletely cured lens and the production of lens defects. Factors thatcontribute to premature release are (1) a poorly assembled lens cell 52;(2) the presence of air bubbles around the sample edges; (3)imperfection in gasket lip or mold edge; (4) inappropriate formulation;(5) uncontrolled temperature rise; and (6) high or nonuniform shrinkage.Preferably, these conditions are minimized.

Premature release may also occur when the opposed mold members 78 areheld too rigidly by the annular gasket 80. Preferably, there issufficient flexibility in the annular gasket 80 to permit the opposedmold members 78 to follow the lens as it shrinks. Indeed, the lens mustbe allowed to shrink in diameter slightly as well as in thickness. Theuse of an annular gasket 80 that has a reduced degree of stickiness withthe lens during and after curing is therefore desirable.

In a preferred technique for filling the lens molding cavity 82, theannular gasket 80 is placed on a concave or front mold member 92 and aconvex or back mold member 90 is moved into place. The annular gasket 80is then pulled away from the edge of the back mold member 90 at theuppermost point and a lens forming composition is injected into the lensmolding cavity 82 until a small amount of the lens forming compositionis forced out around the edge. The excess is then removed, preferably,by vacuum. Excess liquid that is not removed could spill over the faceof the back mold member 90 and cause optical distortion in the finishedlens.

Despite the above problems, the advantages offered by the radiationcured lens molding system clearly outweigh the disadvantages. Theadvantages of a radiation cured system include a significant reductionin energy requirements, curing time and other problems normallyassociated with conventional thermal systems.

The lens forming material may include any suitable liquid monomer ormonomer mixture and any suitable photosensitive initiator. The lensforming material, preferably, does not include any component, other thana photoinitiator, that absorbs ultraviolet light having a wavelength inthe range of 300 to 400 nm. The liquid lens forming material ispreferably filtered for quality control and placed in the lens moldingcavity 82 by pulling the annular gasket 80 away from one of the opposedmold members 78 and injecting the liquid lens forming material into thelens molding cavity 82. Once the lens molding cavity 82 is filled withsuch material, the annular gasket 80 is replaced into its sealingrelation with the opposed mold members 78.

Those skilled in the art will recognize that once the cured lens isremoved from the lens molding cavity 82 by disassembling the opposedmold members 78, the lens can be further processed in a conventionalmanner, such as by grinding its peripheral edge.

According to the present invention a polymerizable lens formingcomposition includes an aromatic-containing bis(allylcarbonate)-functional monomer and at least one polyethylenic-functionalmonomer containing two ethylenically unsaturated groups selected fromacrylyl and methacrylyl. In a preferred embodiment, the compositionfurther includes a suitable photoinitiator. In other preferredembodiments, the composition may include one or morepolyethylenic-functional monomers containing three ethylenicallyunsaturated groups selected from acrylyl and methacrylyl, and a dye.

Aromatic-containing bis(allyl carbonate)-functional monomers which canbe utilized in the practice of the present invention are bis(allylcarbonates) of dihydroxy aromatic-containing material. The dihydroxyaromatic-containing material from which the monomer is derived may beone or more dihydroxy aromatic-containing compounds. Preferably thehydroxyl groups are attached directly to nuclear aromatic carbon atomsof the dihydroxy aromatic-containing compounds. The monomers arethemselves known and can be prepared by procedures well known in the art

The aromatic-containing bis(allyl carbonate)-functional monomers can berepresented by the formula:

in which A₁ is the divalent radical derived from the dihydroxyaromatic-containing material and each R₀ is independently hydrogen,halo, or a C₁-C₄ alkyl group. The alkyl group is usually methyl orethyl. Examples of R₀ include hydrogen, chloro, bromo, fluoro, methyl,ethyl, n-propyl, isopropyl and n-butyl. Most commonly R₀ is hydrogen ormethyl; hydrogen is preferred. A subclass of the divalent radical A1which is of particular usefulness is represented by the formula:

in which each R₁ is independently alkyl containing from 1 to about 4carbon atoms, phenyl, or halo; the average value of each a isindependently in the range of from 0 to 4; each Q is independently oxy,sulfonyl, alkanediyl having from 2 to about 4 carbon atoms, oralkylidene having from 1 to about 4 carbon atoms; and the average valueof n is in the range of from 0 to about 3. Preferably Q ismethylethylidene, viz., isopropylidene.

Preferably the value of n is zero, in which case Al is represented bythe formula:

in which each R₁, each a, and Q are as discussed in respect of FormulaII. Preferably the two free bonds are both in the ortho or parapositions. The para positions are especially preferred.

The dihydroxy aromatic-containing compounds from which A₁ is derived mayalso be polyol-functional chain extended compounds. Examples of suchcompounds include alkaline oxide extended bisphenols. Typically thealkaline oxide employed is ethylene oxide, propylene oxide, or mixturesthereof By way of exemplification, when para, para-bisphenols are chainextended with ethylene oxide, the bivalent radical A₁ may often berepresented by the formula:

where each R₁, each a, and Q are as discussed in respect of Formula II,and the average values of j and k are each independently in the range offrom about 1 to about 4.

The preferred aromatic-containing bis(allyl carbonate)-functionalmonomer is represented by the formula:

and is commonly known as bisphenol A bis(allyl carbonate).

A wide variety of compounds may be used as the polyethylenic functionalmonomer containing two or three ethylenically unsaturated groups. Thepreferred polyethylenic functional compounds containing two or threeethylenically unsaturated groups may be generally described as theacrylic acid esters and the methacrylic acid esters of aliphaticpolyhydric alcohols, such as, for example, the di- and triacrylates andthe di- and trimethacrylates of ethylene glycol, triethylene glycol,tetraethylene glycol, tetramethylene glycol, glycidyl, diethyleneglycol,butyleneglycol, propyleneglycol, pentanediol, hexanediol,trimethylolpropane, and tripropyleneglycol. Examples of specificsuitable polyethylenic—functional monomers containing two or threeethylenically unsaturated groups include trimethylolpropanetriacrylate(TIMTA), tetraethylene glycol diacrylate (TFEGDA), tripropylene glycoldiacrylate (TRPGDA), 1,6hexanedioldimethacrylate (HDDMA), andhexanedioldiacrylate (HDDA).

In general, a photoinitiator for initiating the polymerization of thelens forming composition of the present invention, preferably, exhibitsan ultraviolet absorption spectrum over the 300-400 mm range. Highabsorptivity of a photoinitiator in this range, however, is notdesirable, especially when casting a thick lens. The following areexamples of illustrative photoinitiator compounds within the scope ofthe invention: methyl benzoylformate,2-hydroxy-2-methyl-1-phenylpropan-1-one, 1-hydroxycyclohexyl phenylketone, 2,2-di-sec-butoxyacetophenone, 2,2-diethoxyacetophenone,2,2-diethoxy-2-phenyl-acetophenone, 2,2-dimethoxy-2-phenyl-acetophenone,benzoin methyl ether, benzoin isobutyl ether, benzoin, benzil, benzyldisulfide, 2,4-dihydroxybenzophenone, benzylideneacetophenone,benzophenone and acetophenone. Preferred photoinitiator compounds are1-hydroxycyclohexyl phenyl ketone (which is commercially available fromCiba-Geigy as Irgacure 184), methyl benzoylformate (which iscommercially available from Polysciences, Inc.), or mixtures thereof.

Methyl benzoylformate is a generally preferred photoinitiator because ittends to provide a slower rate of polymerization. The slower rate ofpolymerization tends to prevent excessive heat buildup (and resultantcracking of the lens) during polymerization. In addition, it isrelatively easy to mix liquid methyl benzoylformate (which is liquid atambient temperatures) with many acrylates, diacrylates, and allylcarbonate compounds to form a lens forming composition. The lensesproduced with the methyl benzoylformate photoinitiator tend to exhibitmore favorable stress patterns and uniformity.

A strongly absorbing photoinitiator will absorb most of the incidentlight in the first millimeter of lens thickness, causing rapidpolymerization in that region. The remaining light will produce a muchlower rate of polymerization below this depth and will result in a lensthat has visible distortions. An ideal photoinitiator will exhibit highactivity, but will have a lower extinction coefficient in the usefulrange. A lower extinction coefficient of photoinitiators at longerwavelengths tends to allow the ultraviolet radiation to penetrate deeperinto the reaction system. This deeper penetration of the ultravioletradiation allows photoinitiator radicals to form uniformly throughoutthe sample and provide excellent overall cure. Since the sample can beirradiated from both top and bottom, a system in which appreciable lightreaches the center of the thickest portion of the lens is preferred. Thephotoinitiator solubility and compatibility with the monomer system isalso an important requirement.

An additional consideration is the effect of the photoinitiatorfragments in the finished polymer. Some photoinitiators generatefragments that impart a yellow color to the finished lens. Although suchlenses actually absorb very little visible light, they are cosmeticallyundesirable.

Photoinitiators are often very system specific so that photoinitiatorsthat are efficient in one system may function poorly in another. Inaddition, the initiator concentration to a large extent is dependent onthe incident light intensity and the monomer composition. The identityof the initiator and its concentration are important for any particularformulation. A concentration of initiator that is too high tends to leadto cracking and yellowing of the lens. Concentrations of initiator thatare too low tend to lead to incomplete polymerization and a softmaterial.

Dyes and/or pigments are optional materials that may be present whenhigh transmission of light is not necessary.

The listing of optional ingredients discussed above is by no meansexhaustive. These and other ingredients may be employed in theircustomary amounts for their customary purposes so long as they do notseriously interfere with good polymer formulating practice.

According to a preferred embodiment of the present invention, thepreferred aromatic-containing bis(allyl carbonate) functional monomer,bisphenol A bis(allyl carbonate) is admixed with one or more fasterreacting polyethylenic functional monomers containing two acrylate ormethacrylate groups such as 1,6 hexanediol dimethacrylate (HDDMA), 1,6hexanediol diacrylate (HDDA), tetraethylene glycol diacrylate (TTEGDA),and tripropylene glycol diacrylate (TRPGDA) and optionally apolyethylenic functional monomer containing three acrylate groups suchas trimethylolpropane triacrylate (TMPTA). Generally, compoundscontaining acrylate groups polymerize much faster than those containingallyl groups.

In one embodiment, the lamps 40 generate an intensity at the lampsurface of approximately 4.0 to 7.0 mW/cm² of ultraviolet light havingwavelengths between 300 and 400 nm, which light is very uniformlydistributed without any sharp discontinuities throughout the reactionprocess. Such bulbs are commercially available from Sylvania under thetrade designation Sylvania Fluorescent (F15T8/2052) or SylvaniaFluorescent (F15T8/350BL/18″) GTE.

As noted above, ultraviolet light having wavelengths between 300 and 400nm is preferred because the photoinitiators according to the presentinvention, preferably, absorb most efficiently at this wavelength andthe mold members 78, preferably, allow maximum transmission at thiswavelength.

It is preferred that there be no sharp intensity gradients ofultraviolet radiation either horizontally or vertically through the lenscomposition during the curing process. Sharp intensity gradients throughthe lens may lead to defects in the finished lens.

According to one embodiment of the present invention, the liquid lensforming composition includes bisphenol A bis(allyl carbonate) in placeof DEG-BAC. The bisphenol A bis(allyl-carbonate) monomer has a higherrefractive index than DEG-BAC which allows the production of thinnerlenses which is important with relatively thick positive or negativelenses. The bisphenol A bis(allyl-carbonate) monomer is commerciallyavailable from PPG Industries under the trade name HIRI I or CR-73.Lenses made from this product sometimes have a very slight, barelydetectable, degree of yellowing. A small amount of a blue dye consistingof 9, 10-anthracenedione, 1-hydroxy-4-[(4-methylphenyl)amino] availableas Thermoplast Blue 684 from BASF Wyandotte Corp. is preferably added tothe composition to counteract the yellowing. In addition, the yellowingtends to disappear if the lens is subjected to the above-describedpost-cure heat treatment. Moreover, if not post-cured the yellowingtends to disappear at ambient temperature after approximately 2 months.

TTEGDA, available from Sartomer and Radcure, is a diacrylate monomerthat, preferably, is included in the composition because it is a fastpolymerizing monomer that reduces yellowing and yields a very clearproduct. If too much TTEGDA is included in the most preferredcomposition, i.e. greater than about 25% by weight, however, thefinished lens may be prone to cracking and may be too flexible as thismaterial softens at temperatures above 40° C. If TTEGDA is excludedaltogether, the finished lens may to be brittle.

HDDMA, available from Sartomer, is a dimethacrylate monomer that has avery stiff backbone between the two methacrylate groups. HDDMA,preferably, is included in the composition because it yields a stifferpolymer and increases the hardness and strength of the finished lens.This material is quite compatible with the bisphenol A bis(allylcarbonate) monomer. HDDMA contributes to high temperature stiffness,polymer clarity and speed of polymerization.

TRPGDA, available from Sartomer and Radcure, is a diacrylate monomerthat, preferably, is included in the composition because it providesgood strength and hardness without adding brittleness to the finishedlens. This material is also stiffer than TTEGDA.

TMPTA, available from Sartomer and Radcure, is a triacrylate monomerthat, preferably, is included in the composition because it providesmore crosslinking in the finished lens than the difunctional monomers.TMPTA has a shorter backbone than TTEGDA and increases the hightemperature stiffness and hardness of the finished lens. Moreover, thismaterial contributes to the prevention of optical distortions in thefinished lens. TMPTA also contributes to high shrinkage duringpolymerization. The inclusion of too much of this material in the mostpreferred composition may make the finished lens too brittle.

Certain of the monomers that are preferably utilized in the compositionof the present invention, such as TTEGDA, TRPGDA and TMPTA, includeimpurities and have a yellow color in certain of their commerciallyavailable forms. The yellow color of these monomers is preferablyreduced or removed by passing them through a column of alumina (basic)which includes aluminum oxide powder—basic. After passage through thealumina column, the monomers absorb almost no ultraviolet light. Alsoafter passage through the alumina column differences between monomersobtained from different sources are substantially eliminated. It ispreferred, however, that the monomers be obtained from a source whichprovides the monomers with the least amount of impurities containedtherein. The composition preferably is filtered prior to polymerizationthereof to remove suspended particles.

The composition of the present invention, preferably, may be preparedaccording to the following protocol. Appropriate amounts of HDDMA,TTEGDA, TMPTA and TRPGDA are mixed and stirred thoroughly, preferablywith a glass rod. The acrylate/methacrylate mixture may then be passedthrough a purification column.

A suitable purification column may be disposed within a glass columnhaving a fitted glass disk above a teflon stopcock and having a topreservoir with a capacity of approximately 500 ml and a body with adiameter of 22 mm and a length of about 47 cm. The column may beprepared by placing on the fitted glass disk approximately 35 g. ofactivated alumina (basic), available from ALFA Products, JohnsonMatthey, Danvers, Mass. in a 60 mesh form or from Aldrich in a 150 meshform. Approximately 10 g. of an inhibitor remover(hydroquinone/methylester remover) available as HR-4 from ScientificPolymer Products, Inc., Ontario, N.Y. then may be placed on top of thealumina and, finally, approximately 35 g. of activated alumina (basic)may be placed on top of the inhibitor remover.

Approximately 600 g. of the acrylate/methacrylate mixture may then beadded above the column packing. An overpressure of 2-3 psi may then beapplied to the top of the column resulting in a flow rate ofapproximately 30 to 38 grams per hour. Parafilm may be used to cover thejunction of the column tip and the receiving bottle to prevent theinfiltration of dust and water vapor. The acrylate/methacrylate mixture,preferably, may be received in a container that is opaque to ultravioletradiation.

An appropriate amount of bisphenol A bis(allyl carbonate) may then beadded to the acrylatelmethacrylate mixture to prepare the final monomermixture.

An appropriate amount of a photoinitiator may then be added to the finalmonomer mixture. The final monomer mixture, with or withoutphotoinitiator, may then be stored in a container that is opaque toultraviolet radiation.

An appropriate amount of a dye may also be added to the final monomermixture, with or without photoinitiator.

After edging, the ultraviolet light cured lenses of the presentinvention demonstrate excellent organic solvent resistance to acetone,methylethyl ketone, and alcohols.

For best results, both the casting surfaces 86 and non-casting surfaces88 of the mold members 78 are finished to optical quality. For instance,a wave on the non-casting surface 88 may be reproduced in the finishedlens as a result of the distortion of the incident light.

Mold markings cause differential light intensity conditions under themarking, even when the mark is on the non-casting surface 88 of the moldmembers 78. The fully exposed region of the lens will tend to be harder,and the lens may have stresses because of this. The portion of the lensunder the mark will also tend to be weaker at the end of the curingperiod. This effect has been observed and may cause premature release orinduce cracking.

Mold defects at the edges interfere with the sealing conditions andfrequently induce premature release.

It is believed that as the reaction proceeds, the heat generated tendsto reduce the adhesion between the shrinking lens and the mold face.This reduction in adhesion tends to cause the lens to pull away from themold. In high curvature (i.e. high power) lenses this problem tends tobe even more pronounced because of two factors: (1) these lenses havemore thickness and thus more material that is generating heat (whichthus speeds up the reaction and generates more heat), and (2) theselenses have a greater thickness differential between the thick and thinportions of the lens, which tends to cause stress on the molds due todifferential shrinkage. It is also possible that the temperaturesgenerated relatively deep inside a thick lens may cause somevaporization of the monomer. The vaporized monomer may then migrate tothe lens/mold interface, breaking the vacuum between the two.

Because of the problem of premature release, preferably high powerlenses are cured to maintain adhesion to the molds. Preferably the moldsflex and accommodate stress.

Preferably the cooling fluid used is air at a temperature of less than50° C. The fluid may be below 0° C., however in a preferred embodimentthe fluid was at a temperature of between 0° C. and less than 20° C.,preferably about 0-15° C., more preferably about 0-10° C., morepreferably still about 3-8° C. In one preferred embodiment the fluidtemperature was about 5° C. As shown in FIG. 9, a lens forming apparatus300 for making a plastic lens may include a cooler 312 for supplyingcool fluid to the apparatus 300 via conduit 314. The fluid may besupplied to the apparatus 300 and then discharged via conduit 320. Thefluid discharged via conduit 320 may be vented via conduit 318 or it mayalternately be recirculated via conduit 316 to the cooler 312. Thecooler 312 preferably includes a Neslab CFT-50 water/antifreeze chiller(Newington, N.H., U.S.A.). A Neslab-built blower box designed for aminimum temperature of 3° C. and 8 cubic feet (about 0.224 cubic meters)per minute of air per air distributor 94 was used with the chiller. Theblower box included a heat exchanger coil through which chilled waterwas circulated, a blower, and a plenum-type arrangement for supplyingair to the conduit 314.

If lenses are produced with continuous UV light without any moldcooling, the temperature of the mold-lens assembly may rise to above 50°C. Low diopter lenses may be prepared in this fashion, but higher plusor minus diopter lenses may fail. Certain lenses may be made bycontrolling (e.g., cooling) the temperature of the lens material duringcure with circulating uncooled fluid (i.e., fluid at ambienttemperatures). The ambient fluid in these systems is directed towardsthe mold members in the same manner as described above. Circulatingambient temperature fluid permits manufacture of a wider range ofprescriptions than manufacture of the lenses without any mold cooling atall.

Most polymerization factors are interrelated. The ideal temperature ofpolymerization is related to the diopter and thickness of the lens beingcast. Thermal mass is a factor. Lower temperatures (below about 10° C.)are preferred to cast higher + or − diopter lenses when using continuousUV light. These lower temperatures tend to permit an increase inphotoinitiator concentration, which in turn may speed up the reactionand lower curing time.

Preventing premature release when using continuous UV light is alsosomewhat dependent upon the flowrates of cooling fluid, as well as itstemperature. For instance, if the temperature of the cooling fluid isdecreased it may also be possible to decrease the flowrate of coolingfluid. Similarly, the disadvantages of a higher temperature coolingfluid may be somewhat offset by higher flowrates of cooling fluid.

In one embodiment the air flow rates for a dual distributor system(i.e., an air distributor above and below the lens composition) areabout 1-30 standard cubic feet (“scf”) (about 0.028-0.850 standard cubicmeters) per minute per distributor, more preferably about 4-20 cubicfeet (about 0.113-0.566 standard cubic meters) per minute perdistributor, and more preferably still about 9-15 (about 0.255-0.423standard cubic meters) cubic feet per minute per distributor. “Standardconditions,” as used herein, means 60° F. (about 15.556° C.) and oneatmosphere pressure (about 101.325 kilopascals).

The thickness of the glass molds used to cast polymerized lenses mayaffect the lenses produced. A thinner mold tends to allow more efficientheat transfer between the polymerizing material and the cooling air,thus reducing the rate of premature release. In addition, a thinner moldtends to exhibit a greater propensity to flex. A thinner mold tends toflex during the relatively rapid differential shrinkage between thethick and thin portions of a polymerized lens, again reducing theincidence of premature release. In one embodiment the first or secondmold members have a thickness less than about 5.0 mm, preferably about1.0-5.0 mm, more preferably about 2.0-4.0 mm, and more still about2.5-3.5 mm.

“Front” mold or face means the mold or face whose surface ultimatelyforms the surface of an eyeglass lens that is furthest from the eye ofan eyeglass lens wearer. “Back” mold or face means the mold or facewhose surface ultimately forms the surface of an eyeglass lens that isclosest to the eye of a eyeglass lens wearer.

In one embodiment the lens forming material is preferably cured to forma solid lens at relatively low temperatures, relatively low continuousultraviolet light intensity, and relatively low photoinitiatorconcentrations. Lenses produced as such generally have a Shore Dhardness of about 60-78 (for the preferred compositions) when cured forabout 15 minutes as described above. The hardness may be improved toabout 80-81 Shore D by postcure heating the lens in a conventional ovenfor about 10 minutes, as described above.

In a preferred embodiment, UV light may be provided with mercury vaporlamps provided in UVEXS, Inc. Model CCU or 912 curing chambers(Sunnyvale, Calif., U.S.A.).

In an alternate method for making a lens, the desired curvature (i.e.,power) of the lens may be varied using the same molds, but withdifferent light distributions. In this manner one mold may be used toprepare different lenses with different curvatures. The method includesthe steps of: (1) placing a polymerizable lens forming material in amold cavity defined in part between a first mold member and a secondmold member, and wherein the cavity defines a theoretical curvature thatis different from the desired curvature, (2) directing ultraviolet raystowards at least one of the first and second mold members, and whereinthe ultraviolet rays are directed towards the first or second moldmember such that the material cures to form a lens with the desiredcurvature, and (3) contacting fluid against the first or second moldmember to cool the first or second mold member. The resulting lenscurvature may vary depending on the way the ultraviolet light isdirected towards the first or second mold members. That is, by varyingthe relative intensity of the light across the lens material radii, itis possible to vary the curvature of the resulting lens.

EXAMPLE 1

Formulation: 17% Bisphenol A BisAllyl Carbonate 10% 1,6 Hexanedioldimethacrylate 20% Trimethylolpropane triacrylate 21%Tetraethyleneglycol diacrlate 32% Tripropyleneglycol diacrlyate 0.012% 1Hydroxycyclohexyl phenyl ketone 0.048 Methylbenzoylformate <10 PPMHydroquinone & Methylethylhydroquinone

Hydroquinone and Methylethylhydroquinone were stabilizers present insome of the diacrylate and/or triacrylate compounds obtained fromSartomer. Preferably the amount of stabilizers is minimized since thestabilizers affect the rate and amount of curing. If larger amounts ofstabilizers are added, then generally larger amounts of photoinitiatorsmust also be added.

Light Condition: mW/cm² measured at plane of sample with Spectroline DM365N Meter from Spectronics Corp. (Westbury, N.Y.)

Center Edge Top: 0.233 0.299 Bottom: 0.217 0.248

Air Flow: 9.6 standard cubic feet (“CFM”) per manifold—19.2 CFM total onsample

Air Temperature: 4.4 degrees Centigrade

Molds: 80 mm diameter Corning #8092 glass

Radius Thickness Concave: 170.59 2.7 Convex:  62.17 5.4

Gasket: General Electric SE6035 silicone rubber with a 3 mm thicklateral lip dimension and a vertical lip dimension sufficient to providean initial cavity center thickness of 2.2 mm.

Filling: The molds were cleaned and assembled into the gasket. Themold/gasket assembly was then temporarily positioned on a fixture whichheld the two molds pressed against the gasket lip with about 1 kg. ofpressure. The upper edge of the gasket was peeled back to allow about27.4 grams of the monomer blend to be charged into the cavity. The upperedge of the gasket was then eased back into place and the excess monomerwas vacuumed out with a small aspirating device. It is preferable toavoid having monomer drip onto the noncasting surface of the moldbecause a drop tends to cause the ultraviolet light to become locallyfocused and may cause an optical distortion in the final product.

Curing: The sample was irradiated for fifteen minutes under the aboveconditions and removed from the “FC-104” curing chamber (i.e., thechamber shown in FIGS. 14 and 15). The molds were separated from thecured lens by applying a sharp impact to the junction of the lens andthe convex mold. The sample was then postcured at 110° C. in aconventional gravity type thermal oven for an additional ten minutes,removed and allowed to cool to room temperature.

Results: The resulting lens measured 72 mm in diameter, with a centralthickness of 2.0 mm, and an edge thickness of 9.2 mm. The focusing powermeasured ˜5.05 diopter. The lens was water clear (“water-white”), showednegligible haze, exhibited total visible light transmission of about94%, and gave good overall optics. The Shore D hardness was about 80.The sample withstood the impact of a 1 inch steel ball dropped fromfifty inches in accordance with ANSI 280.1-1987, 4.6.4 test procedures.

ADDITIONAL IMPROVEMENTS POSTCURE WITH AN OXYGEN BARRIER ENRICHED WITHPHOTOINITIATOR

In certain applications, all of the lens forming composition may fail tocompletely cure by exposure to ultraviolet rays when forming the lens.In particular, a portion of the lens forming composition proximate thegasket often remains in a liquid state following formation of the lens.It is believed that the gaskets are often somewhat permeable to air,and, as a result, oxygen permeates them and contacts the portions of thelens forming material that are proximate the gasket. Since oxygen tendsto inhibit the photocuring process, portions of the lens formingcomposition proximate the gasket tend to remain uncured as the lens isformed.

Uncured lens forming composition proximate the gasket is a problem forseveral reasons. First, the liquid lens forming composition leaves theedges of the cured lens in a somewhat sticky state, which makes thelenses more difficult to handle. Second, the liquid lens formingcomposition is somewhat difficult to completely remove from the surfaceof the lens. Third, liquid lens forming composition may flow and atleast partially coat the surface of lenses when such lenses are removedfrom the molds. This coating is difficult to remove and makesapplication of scratch resistant coatings or tinting dyes moredifficult. This coating tends to interfere with the interaction ofscratch resistant coatings and tinting dyes with the cured lens surface.Fourth, if droplets of liquid lens forming material form, these dropletsmay later cure and form a ridge or bump on the surface of the lens,especially if the lens undergoes later postcure or scratch resistantcoating processes. As a result of the above problems, often lenses mustbe tediously cleaned or recast when liquid lens forming compositionremains after the lens is formed in an initial cure process.

The problems outlined above can be mitigated if less liquid lens formingcomposition remains proximate the gasket after the lens is formed. Onemethod of lessening this “wet edge” problem relates to increasing theamount of photoinitiator present in the lens forming composition (i.e.,increasing the amount of photoinitiator in the lens forming compositionabove about 0.15 percent). Doing so, however, tends to create otherproblems. Specifically, increased photoinitiator levels tend to causeexothermic heat to be released at a relatively high rate during thereaction of the composition. Premature release and/or lens crackingtends to result. Thus it is believed that lower amounts ofphotoinitiator are preferred.

The wet edge problem has been addressed by a variety of methodsdescribed in U.S. patent application Ser. No. 07/931,946. Such methodsrelate to removing the gasket and applying either an oxygen barrier or aphotoinitiator enriched liquid to the exposed edge of the lens. The lensis then re-irradiated with sufficient ultraviolet light to completelydry the edge of the lens prior to demolding.

An embodiment of the invention relates to improving the methodsdescribed in the 07/931,946 application. This embodiment relates tocombining an oxygen barrier with a photoinitiator. Specifically, in oneembodiment an oxygen barrier 970 (e.g., a thin strip of polyethylenefilm or the like as shown in FIG. 12) is embedded or impregnated with aphotoinitiator 972. The oxygen barrier is then wrapped around the edgeof a cured lens which is still encased between two molds (but with thegasket removed). While still “in the mold,” the lens is then exposed toultraviolet light, thereby drying its edge. An improvement of thismethod over those previously disclosed is that there is a significantreduction in the UV dosage necessary to bring the lens edge to dryness.

A plastic oxygen barrier film which includes a photoinitiator may bemade by: (a) immersing a plastic film in a solution comprising aphotoinitiator, (b) removing the plastic film from the solution, and (c)drying the plastic film. The solution may include an etching agent.Preferably a surface of the plastic film is etched prior to or whileimmersing the plastic film in the solution.

In one example, thin strips (e.g., about 10 mm wide) of high densitypolyethylene film (approximately 0.013 mm thick) may be soaked in asolution of 97% acetone and 3% Irgacure 184 (a photoinitiatorcommercially available from Ciba Geigy located in Farmingdale, N.J.) forabout five minutes. The polyethylene film may be obtained from TapeSolutions, Inc. (Nashville, Tenn.). In a more preferred embodiment, 0.5%Byk 300 (a flow agent commercially available from Byk Chemie located inWallingford, Conn.) may be included in the soaking solution. It isbelieved that xylene in the Byk 300 tends to etch the surface of thefilm and make the film more receptive to absorption of the Irgacure 184.In a still more preferred embodiment, the treated polyethylene stripsmay be dipped in acetone for about ten seconds to remove excess Irgacure184. Excess photoinitiator may be seen as a white powder which coats thestrips after drying. In either case, the strips are then allowed to airdry before applying them to the edge of the lens as described above.

In one alternate embodiment of the invention, a plastic eyeglass lensmay be made by the following steps: (1) placing a liquid polymerizablelens forming composition in a mold cavity defined by a gasket, a firstmold member, and a second mold member; (2) directing first ultravioletrays toward at least one of the mold members to cure the lens formingcomposition so that it forms a lens with a back face, edges, and a frontface, and wherein a portion of the lens forming composition proximatethe edges of the lens is not fully cured; (3) removing the gasket toexpose the edges of the lens; (4) applying an oxygen barrier whichincludes a photoinitiator around the exposed edges of the lens such thatat least a portion of the oxygen barrier photoinitiator is proximatelens forming composition that is not fully cured; and (5) directingsecond ultraviolet rays towards the lens such that at least a portion ofthe oxygen barrier photoinitiator initiates reaction of lens formingcomposition while the oxygen barrier substantially prevents oxygen fromoutside the oxygen barrier from contacting at least a portion of thelens forming composition. The first and second ultraviolet rays may (a)be at the same or different wavelengths and/or intensities, (b) becontinuous or pulsed, and (c) be from the same or different lightsource.

A purpose of the steps 4-5 is to reduce the amount of uncured liquidlens forming composition that is present when the lens is separated fromthe molds and/or gasket. It has been found that reducing the amount ofliquid lens forming composition is especially advantageous if suchreduction occurs before the molds are separated from the cured lens.Separating the molds from the cured lens may cause uncured liquids to atleast partially coat the lens faces. This coating occurs because uncuredliquid lens forming composition tends to get swept over the faces whenthe molds are separated from the lens. It is believed that curing of thelens tends to create a vacuum between the lens and the mold. Air maysweep over the mold faces to fill this vacuum when the molds areseparated from the lens. This air tends to take liquid lens formingcomposition into the vacuum with it.

In step 4 above, an oxygen barrier which includes a photoinitiator isapplied to the edges or sides of the lens after the gasket is removed.Preferably this oxygen barrier is applied while the lens are stillattached to the molds. In an alternate embodiment this oxygen barrier isalso s applied to the edges or sides of the molds at the same time it isapplied to the sides of the lens. In a preferred embodiment, the sidesof the lenses are first cleaned or wiped to remove at least a portion ofthe uncured liquid lens forming composition before the oxygen barrier isapplied.

After the oxygen barrier is applied, second ultraviolet rays aredirected towards the lens. After the second ultraviolet rays aredirected toward the lens, at least a portion of the liquid lens formingcomposition which was not cured in the initial cure steps is cured. Itis believed that the photoinitiator embedded in the oxygen barrierfacilitates faster and more complete curing of the uncured lens formingcomposition. As such, less second ultraviolet rays are employed, therebylessening the time and energy required in this step. Furthermore, lensquality tends to be enhanced since a lower application of the secondultraviolet rays tends to reduce the potential for lens yellowing.

In a preferred embodiment, substantially all of the remaining liquidlens forming composition is cured after the second ultraviolet rays aredirected toward the lens. More preferably, the lens is substantially dryafter the second ultraviolet rays are directed towards the lens.

After the second ultraviolet rays are directed toward the lens, the lensmay then be demolded. The lens may then be tinted. After the lens isdemolded, a scratch resistant coating may be applied to the lens. In oneembodiment, a scratch resistant coating is applied to the demolded lensby applying a liquid scratch resistant coating composition to a face ofthe lens and then applying ultraviolet rays to this face to cure theliquid scratch resistant coating to a solid.

In an embodiment, the intensity of the ultraviolet rays applied to theface of the lens to cure the liquid scratch resistant coatingcomposition to a solid is about 150-300 mW/cm² at a wave length range ofabout 360-370 nm, and about 50-150 mW/cm² at a wave length range ofabout 250-260 nm. The lens may be heated after removal from the molds,or after application of a scratch resistant coating to the lens.

In a preferred embodiment, the total intensity of the first ultravioletrays directed toward the mold members is less than about 10 mW/cm².

In an embodiment, the intensity of the second ultraviolet rays directedtoward the lens is about 150-300 mW/cm² at a wave length range of about360-370 nm, and about 50-150 mW/cm² at a wave length range of about250-260 nm. Preferably the second ultraviolet rays are directed towardsthe lens for less than about 1 minute.

In a preferred embodiment, the above method may further include theadditional step of directing third ultraviolet rays towards the lensbefore the oxygen barrier is applied. These third ultraviolet rays arepreferably applied before the gasket is removed. Preferably, the secondand third ultraviolet rays are directed toward the back face of the lens(as stated above, the second and third ultraviolet rays are preferablyapplied while this lens is in the mold cavity). The third ultravioletrays are preferably about the same range of intensity as the secondultraviolet rays. The same apparatus may be used for both the second andthird ultraviolet rays.

In a preferred embodiment, the method described above also includes thestep of removing the oxygen barrier from the edges of the lens.

The second and third ultraviolet rays may be repeatedly directed towardsthe lens. For instance, these ultraviolet rays may be applied via alight assembly whereby the lens passes under a light source on a movablestand. The lens may be repeatedly passed under the lights. Repeatedexposure of the lens to the ultraviolet rays may be more beneficial thanone prolonged exposure.

Preferably the oxygen barrier includes a film, and more preferably aplastic, flexible, and/or elastic film. In addition, the oxygen barrieris preferably at least partially transparent to ultraviolet rays so thatultraviolet rays may penetrate the oxygen barrier to cure any remainingliquid lens forming composition. Preferably the oxygen barrier isstretchable and self-sealing. These features make the film easier toapply. Preferably the oxygen barrier is resistant to penetration byliquids, thus keeping any liquid lens forming composition in the moldassembly. Preferably, the oxygen barrier includes a thermoplasticcomposition. It is anticipated that many different oxygen barriers maybe used (e.g., saran wrap, polyethylene, etc.). In one preferredembodiment, the film is “Parafilm M Laboratory Film” which is availablefrom American National Can (Greenwich, Conn., U.S.A.). The oxygenbarrier may also include aluminum foil.

Preferably the oxygen barrier is less than about 1.0 mm thick. Morepreferably the oxygen barrier is 0.01 to 0.10 mm thick, and morepreferably still the oxygen barrier is less than 0.025 mm thick. If theoxygen barrier is too thick, then it may not be readily stretchableand/or conformable, and it may not allow a sufficient amount of light topass through it. If the oxygen barrier is too thin, then it may tend totear.

An apparatus for applying a scratch resistant coating composition to alens and then curing the scratch resistant coating composition isdescribed in U.S. Pat. No. 4,895,102 to Kachel et al. and U.S. Pat. No.3,494,326 to Upton (both of which are incorporated herein by reference).In addition, the apparatus schematically shown in FIG. 10 may also beused to apply the scratch resistant coating.

FIG. 10 depicts an apparatus 600 with a first chamber 602 and a secondchamber 604. This apparatus can be used to apply scratch resistantcoating to a lens, to postcure a lens, or to apply ultraviolet light toa lens mold assembly. The first chamber 602 includes an opening 606through which an operator can apply lenses and lens mold assemblies tothe lens holder 608. Lens holder 608 is partially surrounded by barrier614. First chamber 602 may include an inspection light 610, and anopening 618 in the floor of the chamber.

Lens holder 608 is attached to device 612. It is envisioned that device612 may be a spinning device which would permit the apparatus 600 to beused to apply scratch resistant coatings to lenses. In such case device612 would connect directly to lens holder 608 through a hole in thebottom of barrier 614. In a preferred embodiment, however, device 612just connects the lens holder 608 or barrier 614 to moving device 616.It has been found that a separate spinner (not shown) may provide betterresults for application of scratch resistant coatings to lenses.

Preferably barrier 614 has an interior surface that is made or linedwith an absorbant material such as foam rubber. Preferably thisabsorbant material is disposable and removable. The absorbant materialabsorbs any liquids that fall off the lens holder 608, keeping in theinterior surface of the barrier 614 clean.

In an embodiment, shutter 621 is used to inhibit the ultraviolet lightfrom light assembly 622 from contacting barrier 614. It is preferredthat lens holder 608 be exposed to the ultraviolet light from lightassembly 622 while shutter 621 blocks at least a portion of the lightfrom contacting barrier 614. Shutter 621 may also inhibit any liquidlens forming material that falls from lens holder 606 from curing onbarrier 614. Shutter 621 thus tends to inhibit the formation of flakeson the surface of barrier 614. Shutter 621 operates after barrier 614drops, thus shielding barrier 614 while allowing TV light to contact thesample.

In an embodiment, apparatus 600 may be used to apply a precoat to lensbefore the hardcoat is applied. The precoat may serve to increase the“wettability” of the surface to which the hardcoat is to be applied. Asurfactant has been conventionally employed for this purpose, howeversurfactants tend to affect the volatility and flow characteristics oflens coatings in an unfavorable manner. The precoat may include acetoneand/or Byk 300. Upon even distribution of the hardcoat onto a lens inlens holder 608, the coating may be wiped near the edges of the lens toprevent the formation of excessive flakes during curing.

In another embodiment, the precoat and hardcoat are distributed ontolens holder 608. Ultraviolet light is directed toward the coatings atleast until a gel is formed. A lens forming material may be placed ontop of the gel and cured.

Second chamber 604 includes an opening 620 in its floor. It alsoincludes an ultraviolet light assembly 622, which may include multiplelights and a light reflector.

The apparatus 600 includes an air filtering and distribution system. Airis pulled into a chamber 628 by fans 626 through a filter 624 (thequantity and locations of the fans and filters may vary). The filteredair is distributed by the fans 626 throughout chambers 602, 604, and617. Air flows from point 613 to point 615 via air ducts (not shown) toreach chamber 617. The temperature of the lights and/or the secondchamber may be controlled by turning various fans 629 on and off asneeded to suck air out of chamber 604. Air is distributed from chamber617 through holes 636 that are proximate the lower part of the opening606 in the first chamber 602. Air is also sucked by fans 627 from thefirst chamber 602 to chamber 630 through holes 634 that are proximatethe top part of the opening 606 in the first chamber 602. Thisarrangement tends to prevent contaminants from entering first chamber606. Air is discharged from chamber 630 to the surroundings via fans627.

During use a lens or lens mold assembly may be placed on the lens holder608. A button can be pressed, causing the moving device 616 to movedevice 612, lens holder 604, and the barrier 614 so that they are underthe opening 620 in the second chamber 604. Light is thus applied to thelens or lens mold assembly from light assembly 622. After a set periodof time, the moving device 616 moves everything back to a locationunderneath the opening 618 in the first chamber 602.

The lens holder 608 may include a suction cup connected to a metal bar.The concave surface of the suction cup may be attachable to a face of amold or lens, and the convex surface of the suction cup may be attachedto a metal bar. The metal bar may be attachable to a lens spinner.

The lens holder may also alternately include movable arms and a springassembly which are together operable to hold a lens against the lensholder with spring tension during use.

In an alternate method of the invention, a lens may be cured between twomold members. The gasket may be removed and any remaining liquid lenscomposition may be removed. At this point a mold member may be appliedto a substantially solid conductive heat source. Heat may then beconductively applied to a face of the lens by (a) conductivelytransferring heat to a face of a mold member from the conductive heatsource, and (b) conductively transferring heat through such mold memberto the face of the lens. The oxygen barrier enriched with photoinitiatormay then be applied, and second ultraviolet rays may be directed towardsthe lens to cure the remaining lens forming composition.

OXYGEN BARRIER EXAMPLE #1

A liquid lens forming composition was initially cured as in a processand apparatus similar to that specified in Example 1. The compositionwas substantially the same as specified in Example 1, with the exceptionthat hydroquinone was absent, the concentration ofmethylethylhydroquinone was about 25-45 ppm, the concentration of 1hydroxycyclohexyl phenyl ketone was 0.017 percent, and the concentrationof methylbenzoylformate was 0.068 percent. The composition underwent theinitial 15 minute cure under the “1st UV.” The apparatus wassubstantially the same as described for the above Example 1, with thefollowing exceptions:

1. The air flowrate on each side of the lens mold assembly was estimatedto be about 18-20 cubic feet per minute.

2. The apparatus was modified in that air flowed to and from theopenings 96 and orifices 98 (which were themselves substantiallyunchanged) through a duct behind the lens forming chamber, instead ofthrough pipes (e.g. pipe 12 in FIG. 5). Essentially plenum portion 95was expanded so that the walls of the chamber are the walls of theplenum portion 95. FIG. 14 depicts a front view of this lens curingapparatus 800. Air in apparatus 800 flows from the orifices 98, over thelens mold assembly 802, through ducts 804, through fan 806, through heatexchanger 808, and then through ducts 810 and back to orifices 98 viaair return conduits 824 (shown on FIG. 15). FIG. 14 also shows a waterchiller 812 which cools water and then sends it through conduits 814 andthrough heat exchanger 808. FIG. 14 also shows lights 816 and frostedglass 818. The chamber 820 surrounding lights 816 is not connected tothe chamber 822 around the mold assembly 802. In this manner chilled airfrom orifices 98 does not contact and cool the lights 816 (such coolingtends to cause excessive changes in light output). The chamber 820 iscooled by fans (not shown) which turn on and off depending on thetemperature of the surface of the lights 816. FIG. 15 shows a side viewof apparatus 800.

3. The air flowrate in and out of the chamber surrounding the lights wasvaried in accordance with the surface temperature of lights. The airflowrate was varied in an effort to keep the temperature on the surfaceof one of the lights between 104.5° F. and 105° F.

4. The ultraviolet light output was controlled to a set point by varyingthe power sent to the lights as the output of the lights varied.

5. Frosted glass was placed between the lights and the filters used tovary the intensity of the ultraviolet light across the face of themolds. Preferably the glass was frosted on both sides. The frosted glassacts as a diffuser between the lights and these filters. This frostedglass tended to yield better results if it was placed at least about 2mm from the filter, more preferably about 10-15 mm, more preferablystill about 12 mm, from the filter. Frosted glass was found to dampenthe effect of the filters. For instance, the presence of the frostedglass reduced the systems' ability to produce different lens powers byvarying the light (see Example 1 and FIG. 1).

6. In FIG. 3 the center lights 40 are shown in a triangular arrangementwhen viewed from the side. These lights were rearranged to provide anin-line arrangement.

After initial cure, the lens mold assembly was removed from the curingchamber. The lens mold assembly included a lens surrounded by a frontmold, a back mold, and a gasket between the front and back molds (see,e.g., the assembly in FIG. 6).

At this point the protocol in Example 1 stated that the lens wasdemolded (see above). While demolding at this point is possible, asstated above generally some liquid lens forming composition remained,especially in areas of the lens proximate the gasket. Therefore the lenswas not demolded as stated in Example 1. Instead, the gasket wasremoved, liquid lens forming composition was wiped off the edges of thelens, and a layer of oxygen barrier (Parafilm M) with photoinitiator waswrapped around the edges of the lens while the lens was still betweenthe molds. The Parafilm M was wrapped tightly around the edges of thelens and then stretched so that it would adhere to the lens and molds(i.e. in a manner similar to that of Saran wrap). The lens mold assemblywas then placed in apparatus 600 so that the back face of the lens(while between the molds) could then be exposed to second ultravioletlight.

This second ultraviolet light was at a substantially higher intensitythan the initial cure light, which was directed at an intensity of lessthan 10 mW/cm². The mold assembly was passed in and out of secondchamber 604 in FIG. 10 (i.e., a UVEXS Model 912) when the light was setat the high setting. Passing in and out of the chamber took about 22seconds. The total light energy applied during these 22 seconds wasabout 4500 millijoules per square centimeter (“mJ/cm²”).

Preferably the total light energy applied per pass under the second andthird ultraviolet ray lights was in the range of about 500-10,000mJ/cm², more preferably about 3000-6000 MJ/cm², and more preferablystill 4000-5000 mJ/cm². Light energy may be varied by varying the timeof exposure, or the intensity of the light. Light energy was measuredwith a Model IL390B Light Bug from International Light, Inc.(Newburyport, Mass., U.S.A.). The total light energy represents thetotal amount of ultraviolet light over the range of 250 to 400 nm.

It has been found that applying ultraviolet light at this point helpedto cure some or all of the remaining liquid lens forming composition.The second ultraviolet light step may be repeated. In this example thesecond ultraviolet light step was repeated once. It is also possible toexpose the front or both sides of the lens to the second ultravioletlight.

After the second ultraviolet light was applied, the mold assembly wasallowed to cool. The reactions caused by exposure to ultraviolet lightare exothermic. The ultraviolet lights also tend to emit infra-red lightwhich in turn heats the mold assembly. The lens was then demolded. Thedemolded lens was substantially drier and harder than lenses that aredirectly removed from mold assemblies after the initial cure step.

OXYGEN BARRIER EXAMPLE #2

The protocol of Oxygen Barrier Example #1 was repeated except that priorto removal of the gasket the lens mold assembly was positioned so thatthe back face of the lens was exposed to third ultraviolet light. Inthis case the third ultraviolet light was at the same intensity and forthe same time period as one pass of the second ultraviolet light. It hasbeen found that applying third ultraviolet light at this point helped tocure some or all of the remaining liquid lens forming composition sothat when the gasket was removed less liquid lens forming compositionwas present. All of the remaining steps in Oxygen Barrier Example #1were applied, and the resultant lens was substantially dry when removedfrom the molds.

CONDUCTIVE HEATING

An embodiment of the invention relates to postcuring a polymerized lenscontained in a mold cavity by applying conductive heat to at least oneof the molds that form the mold cavity, prior to demolding the lens.

More particularly, one embodiment of the invention includes thefollowing: (1) placing a liquid lens forming composition in a moldcavity defined by at least a first mold member and a second mold member,(2) directing ultraviolet rays toward at least one of the mold membersto cure the lens forming composition so that it forms a lens with a backface, edges, and a front face, (3) applying a mold member of the moldcavity to a substantially solid conductive heat source; and (4)conductively applying heat to a face of the lens by (a) conductivelytransferring heat to a face of a mold member from the conductive heatsource, and (b) conductively transferring heat through such mold memberto the face of the lens.

In an embodiment described as follows, a lens cured by exposure toultraviolet light is further processed by conductive heating. Suchconductive heating tends to enhance the degree of cross-linking in thelens and to increase the tintability of the lens. A lens formingmaterial is placed in mold cavity 900 (illustrated in FIG. 19), which isdefined by at least first mold member 902 and second mold member 904.Ultraviolet rays are directed toward at least one of the mold members,thereby curing the lens forming material to a lens. Heat distributor 910(shown in FIG. 16) may be adapted to distribute conductive heat fromconductive heat source 912 to at least one mold member. Heat distributor910 is preferably flexible such that at least a portion of it may beshaped to substantially conform to the shape of face 906 or face 907 offirst mold member 902 or second mold member 904, respectively. Heatdistributor 910 is preferably placed in contact with conductive heatsource 912, and mold member 902 is placed on heat distributor 910 suchthat face 906 of the mold member rests on top of the heat distributor910. Heat distributor 910 may be coupled to heat source 912. Heat isconductively applied to the heat distributor 910 by the heat source 912.Heat is conducted from the heat distributor 910 through the mold memberto a face of the lens. The heat distributor may be shaped to accommodateface 906 of first mold member 902 or face 907 of second mold member 904such that the heat is applied to front face 916 or back face 915 of thelens (shown in FIG. 11). The temperature of heat source 912 may bethermostatically controlled.

In an embodiment, hot plate 918 (shown in FIG. 17) is used as a heatsource to provide conductive heat to the lens. A number of other heatsources may be used. In an embodiment, heat distributor 910 may includecountershape 920. Countershape 920 may be placed on top of the hot plateto distribute conductive heat from the hot plate. The countershape ispreferably flexible such that at least a portion of it may substantiallyconform to the shape of an outside face of a mold member. Thecountershape may be hemispherical and either convex or concave dependingupon whether the surface of the mold assembly to be placed upon it isconvex or concave. For example, when the concave surface of the backmold is utilized to conduct heat into the lens assembly, a convexcountershape is provided to rest the assembly on.

Countershape 920 may include a glass mold, a metal optical lap, a pileof hot salt and/or sand, or any of a number of other devices adapted toconduct heat from heat source 912. It should be understood that FIG. 17includes combinations of a number of embodiments for illustrativepurposes. Any number of identical or distinct countershapes may be usedin combination on top of a heat source. In an embodiment, a countershapeincludes a container 922 filled with particles 924. The particlespreferably include metal or ceramic material. Countershape 920 mayinclude heat distributor 910. A layer 914 of material may be placed overthe countershape 920 or heat distributor 910 to provide slow, smooth,uniform heat conduction into the lens mold assembly. This layerpreferably has a relatively low heat conductivity and may be made ofrubber, cloth, Nomex™ fabric or any other suitable material thatprovides slow, smooth, uniform conduction.

In an embodiment, countershape 920 includes layer 914 (e.g., a bag orcontainer) filled with particles 924 such that the countershape may beconveniently shaped to conform to the shape of face 906 or face 907. Inan embodiment, the countershape is essentially a “beanbag” that containsparticles 924 and is conformable to the shape of a mold face placed ontop of it. Particles 924 may include ceramic material, metal material,glass beads, sand and/or salt. The particles preferably facilitateconductive heat to be applied to face 906 or face 907 substantiallyevenly.

In an embodiment, the countershape 920 is placed on top of heat source912 for a sufficient time for a portion of the countershape to attain atemperature substantially near or equal to the temperature on thesurface of the heat source. The countershape may then be “flipped over”such that the heated portion of the countershape that has a temperaturesubstantially near or equal to that of the surface of the heat source isexposed. A mold may be placed on top of the heated portion of thecountershape, and the countershape is preferably conformed to the shapeof the face of the mold. In this manner, the rate of conductive heattransfer to the lens may begin at a maximum. Heat is preferablyconductively transferred through the countershape and the mold face to aface of the lens. The temperature of the heated portion of thecountershape may tend to decrease after the mold is placed onto thecountershape.

In an embodiment, heat distributor 910 may partially insulate a moldmember from conductive heat source 912. The heat distributor preferablyallows a gradual, uniform transfer of heat to the mold member. The heatdistributor is preferably made of rubber and/or another suitablematerial. The heat distributor may include countershapes of variousshapes (e.g., hemispherically concave or convex) and sizes that areadapted to contact and receive mold members.

In an embodiment, hot plate cover 930 (shown in FIG. 8) is used todistribute conductive heat to face 906 of mold member 902. Cover 930 isadapted to rest directly upon hot plate 918 (or any other heat source).Cover 930 preferably includes portion 932, which is substantiallyconformed to the shape of face 906. Portion 932 preferably includes aconvex surface or a concave surface (not shown) adapted to receive face906. Portion 932 is preferably made of rubber and causes slow, uniformtransfer of conductive heat to face 906. In an embodiment, a hot platecover having concave indentations substantially conformed to the shapeof face 907 is used to distribute heat through a mold member to a lens.

In an embodiment, heat is conductively applied by the heat source toonly one outside face of one mold member. This outside face may be face906 or face 907. Heat may be applied to back face 915 of the lens toenhance crosslinking and/or tintability of the lens material proximateto the surface of the back face of the lens.

In a preferred embodiment, thermostatically controlled hot plate 918 isused as a heat source. Glass optical mold 928 is preferably placedconvex side up on hot plate 918 to serve as a countershape. The glassoptical mold preferably has about an 80 mm diameter and a radius ofcurvature of about 93 mm. Rubber disc 929 may be placed over this mold928 to provide uniform conductive heat to the lens mold assembly. Therubber disc is preferably made of silicone and preferably has a diameterof approximately 74 mm and a thickness of about 3 mm. The lens moldassembly preferably is placed on mold 928 so that outside face 906 of amold member of the assembly rests on top of mold 928. It is preferredthat the edge of the lens mold assembly not directly contact the hotplate. The lens mold assembly preferably receives heat through therubber disc and not through its mold edges.

To achieve good yield rates and reduce the incidence of prematurerelease while using the conductive heat method, it may be necessary forthe edge of the lens be completely cured and dry before conductive heatis applied. If the lens edge is incompletely cured (i.e., liquid or gelis still present) while conductive heat is applied, there may be a highincidence of premature release of the lens from the heating unit.

In an embodiment, the edges of a lens are treated to cure or removeincompletely cured lens forming material (see above description) beforeconductive heat is applied. The mold cavity may be defined by at leastgasket 908, first mold member 902, and second mold member 904.Ultraviolet rays are directed toward at least one of the mold members,thereby curing the lens forming material to a lens preferably havingfront face 916, a back face 915, and edges. Upon the formation of thelens, the gasket may be removed from the mold assembly. An oxygenbarrier may be used to cure any remaining liquid or gel on the lens edgeaccording to any of the methods of the above-detailed embodiments. Anoxygen barrier treated with photoinitiator is preferably employed.Alternatively, any remaining liquid or gel may be removed manually. Oncethe edge of the lens is dry, a face of the lens may be conductivelyheated using any of the methods described herein.

In an embodiment, a lens is tinted after receiving conductive heatpostcure treatment in a mold cavity. During tinting of the lens, thelens is preferably immersed in a dye solution.

CONDUCTIVE HEATING EXAMPLE

A liquid lens forming composition was initially cured in a process andapparatus similar to that specified in Example 1 except for post-curetreatment which was conducted as follows:

After the sample was irradiated for 15 minutes, the lens was removedfrom the FC-104 chamber and then passed through the above-mentionedUVEXS Model 912 curing chamber (see FIG. 10) to receive a dose of about1500 mJ/cm² (+/−100 mJ) of ultraviolet light per pass. The gasket wasthen removed from the mold assembly and the edges of the mold were wipedwith an absorbent tissue to remove incompletely cured lens formingmaterial proximate the mold edges. A strip of plastic materialimpregnated with photoinitiator was wrapped around the edges of themolds that were exposed when the gasket was removed. Next, the moldassembly was passed through the UVEXS curing chamber once to expose thefront surface of the mold to a dose of about 1500 mJ/cm². The moldassembly was then passed through the UVEXS four more times, with theback surface of the mold receiving a dose of about 1500 mJ/cm² per pass.A hot plate was operated such that the surface of the hot plate reacheda temperature of 340 degrees F (+/−50 degrees F). A conformable“beanbag” container having a covering made of Nomex™ fabric was placedon the hot plate. The container contained glass beads and was turnedover such that the portion of the container that had directly contactedthe hot plate (i.e., the hottest portion of the container) faced upwardand away from the hot plate. The mold assembly was then placed onto theheated, exposed portion of the container that had been in direct contactwith the hot plate. The concave, non-casting face of the mold was placedonto the exposed surface of the container which substantially conformedto the shape of the face. Heat was conducted through the container andthe mold member to the lens for 13 minutes. A lens having a Shore Dhardness of 84 was formed.

PULSED ULTRAVIOLET LIGHT APPLICATION

A polymerizable lens forming composition may be placed in a mold/gasketassembly and continuously exposed to appropriate levels of ultravioletlight to cure the composition to an optical lens. The progress of thecuring reaction may be determined by monitoring the internal temperatureof the composition. The lens forming composition may be considered topass through three stages as it is cured: (1) Induction, (2) GelFormation & Exotherm, and (3) Extinction. These stages are illustratedin FIG. 20 for a −0.75−1.00 power lens cured by continuous applicationof UV light. FIG. 20 shows temperature within the mold cavity as afunction of time throughout a continuous radiation curing cycle.

The induction stage occurs at the beginning of the curing cycle and istypically characterized by a substantially steady temperature (orfalling temperature when the curing chamber temperature is below that ofthe composition) of the lens forming composition as it is irradiatedwith ultraviolet light. During the induction period, the lens formingcomposition remains in a liquid state as the photoinitiator breaks downand consumes inhibitor and dissolved oxygen present in the composition.As the inhibitor content and oxygen content of the composition fall,decomposing photoinitiator and the composition begin to form chains toproduce a pourable, “syrup-like” material.

As irradiation continues, the “syrup” proceeds to develop into a soft,non-pourable, viscous, gel. A noticeable quantity of heat will begin tobe generated during this soft gel stage. The optical quality of the lensmay be affected at this point. Should there be any sharp discontinuitiesin the intensity of the activating ultraviolet light (for example, adrop of composition on the exterior of a mold which focuses light into aportion of the lens forming composition proximate the drop), a localdistortion will tend to be created in the gel structure, likely causingan aberration in the final product. The lens forming composition willpass through this very soft gel state and through a firm gel state tobecome a crystalline structure. When using OMB-91 lens formingcomposition, a haze tends to form momentarily during the transitionbetween the gel and crystalline stages. As the reaction continues andmore double bonds are consumed, the rate of reaction and the rate ofheat generated by the reaction will slow, which may cause the internaltemperature of the lens forming composition to pass through a maximum atthe point where the rate of heat generation exactly matches the heatremoval capacity of the system.

By the time the maximum temperature has been reached and the lensforming composition begins to cool, the lens will typically haveachieved a crystalline form and will tend to crack rather than crumbleif it is broken. The rate of conversion will slow dramatically and thelens may begin to cool even though some reaction still may be occurring.Irradiation may still be applied through this extinction phase.Generally, the curing cycle is assumed to be complete when thetemperature of the lens forming composition falls to a temperature nearits temperature at the beginning of exotherm (i.e., the point where thetemperature of the composition increased due to the heat released by thereaction).

The continuous irradiation method tends to work well for relatively lowmass lenses (up to about 20-25 grams) under the FC-104 curing chamberconditions (see, e.g., U.S. Pat. Nos. 5,364,256 and 5,415,816). As theamount of material being cured increases, problems may be encountered.The total amount of heat generated during the exothermic phase issubstantially proportional to the mass of the lens forming material.During curing of relatively high mass lenses, a greater amount of heatis generated per a given time than during curing of lower mass lenses.The total mold/gasket surface area available for heat transfer (e.g.,heat removal from the lens forming composition), however, remainssubstantially constant. Thus the internal temperature of a relativelyhigh mass of lens forming material may rise to a higher temperature morerapidly than typically occurs with a lower mass of lens formingmaterial. For example, the internal temperature of a low minuscast-to-finish lens typically will not exceed about 100° F., whereascertain thicker semi-finished lens “blanks” may attain temperaturesgreater than about 350° F. when continually exposed to radiation. Thelens forming material tends to shrink as curing proceeds and the releaseof excessive heat during curing tends to reduce the adhesion between themold and the lens forming material. These factors may lead to persistentproblems of premature release and/or cracking during the curing of lensforming material having a relatively high mass.

A significant advantage of the present invention is the production ofrelatively high-mass, semi-finished lens blanks and high powercast-to-finish lenses without the above-mentioned problems of prematurerelease and cracking. Methods of the present invention as describedbelow allow even more control over the process of curing ophthalmiclenses with ultraviolet light-initiated polymerization than previousmethods. By interrupting or decreasing the activating light at theproper time during the cycle, the rate of heat generation and releasecan be controlled and the incidence of premature release can be reduced.An embodiment of the invention relates to a method of controlling therate of reaction (and therefore the rate of heat generation) of a UVlight-curable, lens forming material by applying selected intermittentdoses (e.g., pulses) of radiation followed by selected periods ofdecreased UV light or “darkness”. It is to be understood that in thedescription that follows, “darkness” refers to the absence of activatingradiation, and not necessarily the absence of visible light.

More particularly, an embodiment of the invention relates to: (a) aninitial exposure period of the lens forming material to radiation (e.g.,continuous or pulsed radiation) extending through the induction period,(b) interrupting or decreasing the irradiation before the materialreaches a first temperature (e.g., the maximum temperature thecomposition could reach if irradiation were continued) and allowing thereaction to proceed to a second temperature lower than the firsttemperature, and (c) applying a sufficient number of alternating periodsof exposure and decreased UV light or darkness to the lens formingmaterial to complete the cure while controlling the rate of heatgeneration and/or dissipation via manipulation of the timing andduration of the radiation, or the cooling in the curing chamber. FIG. 21shows the temperature within the mold cavity as a function of time forboth (a) continuous ultraviolet light exposure and (b) pulsedultraviolet light exposure.

In the context of this application, a “gel” occurs when the liquid lensforming composition is cured to the extent that it becomes substantiallynon-pourable, yet is still substantially deformable and substantiallynot crystallized.

In the following description, it is to be understood that the term“first period” refers to the length of time of the initial exposureperiod where radiation (e.g., in pulses) is applied to the lens formingcomposition, preferably to form at least a portion of the compositioninto a gel. “First ultraviolet” rays or light refers to the radiationapplied to the lens forming composition during the initial exposureperiod. “Second ultraviolet” rays or light refers to the radiation thatis applied to the lens forming composition (e.g., in pulses) after thecomposition has been allowed to cool to the “third temperature”mentioned above. “Second period” refers to the duration of time thatsecond ultraviolet rays are directed to the lens forming composition.“Third period” refers to the duration of decreased UV light or darknessthan ensues after UV light has been delivered in the second period.

In an embodiment of the invention, the lens forming material is placedin a mold cavity defined in part between a first mold member and asecond mold member. The first mold member and/or second mold member mayor may not be continuously cooled as the formation of the lens iscompleted during the second period and/or third period. One method ofremoving heat from the lens forming material is to continuously directair at a non-casting face of at least one of the mold members. It ispreferred that air be directed at both the first and second moldmembers. A cooler may be used to cool the temperature of the air to atemperature below ambient temperature, more preferably between about 0°C. and about 20° C., and more preferably still between about 3° C. andabout 15° C. Air may also be used to cool at least one of the moldmembers (in any of the manners described previously) during the firstperiod.

In an embodiment of the invention, the first period ends when at least aportion of the lens forming composition begins to increase intemperature or form a gel, and the first ultraviolet rays are decreasedor removed (e.g., blocked) such that they cease to contact the first orsecond mold members. It is preferred that the first period be sufficientto allow the lens forming material to gel in the mold cavity such thatthere is substantially no liquid present (except small amounts proximatethe edge of the material). The interruption of irradiation prior tocomplete gelation may in some circumstances produce optical distortions.It is preferred that the length of the first period be selected toinhibit the lens forming composition from reaching a first temperature.The first temperature is preferably the maximum temperature that thelens forming composition could reach if it was irradiated under thesystem conditions (e.g., flow rate and temperature of any cooling air,wavelength and intensity of radiation) until the “exothermic potential”(i.e., ability to evolve heat through reaction) of the composition wasexhausted.

According to an embodiment of the invention, the reactions within thecomposition are allowed to proceed after the first ultraviolet rays areremoved until the composition reaches a second temperature. The secondtemperature is preferably less than the first temperature. The firsttemperature is preferably never reached by the composition. Thus,preferably the composition is prevented from achieving the firsttemperature and then cooling to the second temperature. The compositionpreferably is allowed to cool from the second temperature to the thirdtemperature. This cooling may occur “inactively” by allowing heat totransfer to the ambient surroundings, or at least one of the moldmembers may be cooled by any of the methods described above.

In an embodiment of the invention, the curing of the lens formingmaterial is completed by directing second ultraviolet rays (e.g., inpulses) toward at least one of the mold members. The second UV rays maybe directed toward the mold member(s) for a second period that may bedetermined according to the rate of reaction of the lens formingcomposition. The change in temperature of the composition or a portionof the mold cavity, or the air in or exiting the chamber is an indicatorof the rate of reaction, and the second period may be determinedaccordingly. The second period may be varied such that subsequent pulseshave a longer or shorter duration than previous pulses. The time betweenpulses (i.e., the third period) may also be varied as a function of thetemperature and/or reaction rate of the composition. To achieve a lightpulse, (a) the power to a light source may be turned on and then off,(b) a device may be used to alternately transmit and then block thepassage of light to the lens forming composition, or (c) the lightsource and/or mold assembly may be moved to inhibit ultraviolet lightfrom contacting the lens forming material. The second and/or thirdperiods are preferably controlled to allow rapid formation of a lenswhile reducing the incidence of (a) premature release of the lens fromthe first and/or second mold member and/or (b) cracking of the lens.

In an embodiment, the second period is preferably controlled to inhibitthe temperature of the composition from exceeding the secondtemperature. The temperature of the lens forming composition maycontinue to increase after radiation is removed from the first and/orsecond mold members due to the exothermic nature of reactions occurringwithin the composition. The second period may be sufficiently brief suchthat the pulse of second ultraviolet rays is removed while thetemperature of the composition is below the second temperature, and thetemperature of the composition increases during the third period tobecome substantially equal to the second temperature at the point thatthe temperature of the composition begins to decrease.

In an embodiment, the third period extends until the temperature of thecomposition becomes substantially equal to the third temperature. Oncethe temperature of the composition decreases to the third temperature, apulse of second ultraviolet rays may be delivered to the composition. Inan embodiment, the second period remains constant, and the third periodis controlled to maintain the temperature of the composition below thesecond temperature. The third period may be used to lower thetemperature of the composition to a temperature that is expected tocause the composition to reach but not exceed the second temperatureafter a pulse is delivered to the composition.

In an embodiment, shutter system 950 (shown in FIG. 7) is used tocontrol the application of first and/or second ultraviolet rays to thelens forming material. Shutter system 950 preferably includesair-actuated shutter plates 954 that may be inserted into the curingchamber to prevent ultraviolet light from reaching the lens formingmaterial. Shutter system 950 may include programmable logic controller952, which may actuate air cylinder 956 to cause shutter plates 954 tobe inserted or extracted from the curing chamber. Programmable logiccontroller 952 preferably allows the insertion and extraction of shutterplates 954 at specified time intervals. Programmable logic controller952 may receive signals from thermocouple(s) located inside chamber,proximate at least a portion the mold cavity, or located to sense thetemperature of air in or exiting the chamber, allowing the timeintervals in which the shutters are inserted and/or extracted to beadjusted as a function of a temperature within the curing chamber. Thethermocouple may be located at numerous positions proximate the moldcavity and/or casting chamber.

The wavelength and intensity of the second ultraviolet rays arepreferably substantially equal to those of the first ultraviolet rays.It may be desirable to vary the intensity and/or wavelength of theradiation (e.g, first or second ultraviolet rays). The particularwavelength and intensity of the radiation employed may vary amongembodiments according to such factors as the identity of the compositionand curing cycle variables.

Numerous curing cycles may be designed and employed. The design of anoptimal cycle should include consideration of a number of interactingvariables. Significant independent variables include: 1) the mass of thesample of lens forming material, 2) the intensity of the light appliedto the material, 3) the physical characteristics of the lens formingmaterial, and 4) the cooling efficiency of the system. Significantcuring cycle (dependent) variables include: 1) the optimum initialexposure time for induction and gelling, 2) the total cycle time, 3) thetime period between pulses, 4) the duration of the pulses, and 5) thetotal exposure time.

Most of the experiments involving methods of the present invention wereconducted using below described OMB-91 monomer and the above-mentionedFC-104 curing chamber set at an operating temperature of 55 degrees F,although tests have been performed using other lens forming materialsand curing chamber temperatures. The OMB-91 formulation and propertiesare listed below.

OMB-91 FORMULATION

INGREDIENT WEIGHT PERCENT Sartomer SR 351 (Trimethylolpropane 20.0 +/−1.0 Triacrylate) Sartomer SR 268 (Tetraethylene Glycol 21.0 +/− 1.0Diacrylate) Sartomer SR 306 (Tripropylene Glycol 32.0 +/− 1.0Diacrylate) Sartomer SR 239 (1,6 Hexanediol 10.0 +/− 1.0 Dimethacrylate)(Bisphenol A Bis(Allyl Carbonate)) 17.0 +/− 1.0 Irgacure 184(1-Hydroxycyclohexyl  0.017 +/− 0.0002 Phenyl Keytone) Methyl BenzoylFormate  0.068 +/− 0.0007 Methyl Ester of Hydroquinone (“MeHQ”)  35 ppm+/− 10 ppm Thermoplast Blue P (9,10 - 0.35 ppm +/− 0.1 ppmAnthracenedione, 1-hydroxy-4- ((4-methyl phenyl) Amino)

MEASUREMENTS/PROPERTIES

PROPERTY PROPOSED SPECIFICATION Appearance Clear Liquid Color (APHA) 50maximum (Test Tube Test) Match Standard Acidity (ppm as Acrylic Acid)100 maximum Refractive Index 1.4725 +/− 0.002 Density 1.08 +/− 0.005gm/cc. at 23 degrees C. Viscosity @ 22.5 Degrees C. 27.0 +/− 2centipoise Solvent Weight (wt %) 0.1 Maximum Water (wt %) 0.1 MaximumMeHQ (from HPLC) 35 ppm +/− 10 ppm

It is recognized that methods and systems of the present invention couldbe applied to a large variety of radiation-curable, lens formingmaterials in addition to those mentioned herein. It should be understoodthat adjustments to curing cycle variables (particularly the initialexposure time) may be required even among lens forming compositions ofthe same type due to variations in inhibitor levels among batches of thelens forming compositions. In addition, changes in the heat removalcapacity of the system may require adjustments to the curing cyclevariables (e.g. duration of the cooling periods between radiationpulses). Changes in the cooling capacity of the system and/or changes incompositions of the lens forming material may require adjustments tocuring cycle variables as well.

Significant variables impacting the design of a pulsed curing cycleinclude (a) the mass of the material to be cured and (b) the intensityof the light applied to the material. A significant aspect of methods ofthe present invention is the initial exposure period. If a sample isinitially overdosed with radiation, the reaction may progress too farand increase the likelihood of premature release and/or cracking. If asample is underdosed initially in a fixed (i.e., preset) curing cycle,subsequent exposures may cause too great a temperature rise later in thecycle, tending to cause premature release and/or cracking. Additionally,if the light intensity varies more than about +/−10% in a cycle that hasbeen designed for a fixed light intensity level and/or fixed mass oflens forming material, premature release and/or cracking may result.

An embodiment of the present invention involves a curing cycle havingtwo processes. A first process relates to forming a dry gel bycontinuously irradiating a lens forming composition for a relativelylong period. The material is then cooled down to a lower temperatureunder darkness. A second process relates to controllably discharging theremaining exothermic potential of the material by alternately exposingthe material to relatively short periods of irradiation and longerperiods of decreased irradiation (e.g., dark cooling).

The behavior of the lens forming material during the second process willdepend upon the degree of reaction of the lens forming material that hasoccurred during the first process. For a fixed curing cycle, it ispreferable that the extent of reaction occurring in the first processconsistently fall within a specified range. If the progress of reactionis not controlled well, the incidence of cracking and/or prematurerelease may rise. For a curing cycle involving a composition having aconstant level of inhibitor and initiator, the intensity of theradiation employed is the most likely source of variability in the levelof cure attained in the first process. Generally, a fluctuation of +/−5%in the intensity tends to cause observable differences in the cure levelachieved in the first process. Light intensity variations of +/−10% maysignificantly reduce yield rates.

The effect of various light intensities on the material being cureddepends upon whether the intensity is higher or lower than a preferredintensity for which the curing cycle was designed. FIG. 23 showstemperature profiles for three embodiments in which different lightlevels were employed. If the light intensity to which the material isexposed is higher than the preferred intensity, the overdosage may causethe reaction to proceed too far. In such a case, excessive heat may begenerated, increasing the possibility of cracking and/or prematurerelease during the first process of the curing cycle. If prematurerelease or cracking of the overdosed material does not occur in thefirst process, then subsequent pulses administered during the secondprocess may create very little additional reaction.

If the light intensity is lower than the preferred intensity and thelens forming material is underdosed, other problems may arise. Thematerial may not be driven to a sufficient level of cure in the firstprocess. Pulses applied during the second process may then causerelatively high amounts of reaction to occur, and the heat generated byreaction may be much greater than the heat removal capacity of thesystem. Thus the temperature of the lens forming material may tend toexcessively increase. Premature release may result. Otherwise,undercured lenses that continue generating heat after the end of thecycle may be produced.

The optimal initial radiation dose to apply to the lens forming materialmay depend primarily upon its mass. The initial dose is also a functionof the light intensity and exposure time. A method for designing acuring cycle for a given mold/gasket/monomer combination may involveselecting a fixed light intensity.

Methods of the present invention may involve a wide range of lightintensities. Using a relatively low intensity may allow for the lengthof each cooling step to be decreased such that shorter and morecontrollable pulses are applied. Where a fluorescent lamp is employed,the use of a lower intensity may allow the use of lower power settings,thereby reducing the load on the lamp cooling system and extending thelife of the lamp. A disadvantage of using a relatively low lightintensity is that the initial exposure period tends to be somewhatlonger. Relatively high intensity levels tend to provide shorter initialexposure times while placing more demand upon the lamp drivers and/orlamp cooling system, either of which tends to reduce the life of thelamp.

In an embodiment, General Electric F15T8BL lamps powered by MercronHR0696-4 drivers may be used in conjunction with an FC 104 curingchamber having one piece of double-frosted diffusing glass and one pieceof clear PO-4 acrylic plate. The light intensity settings may be 760microwatts/cm for the top lamps and 950 microwatts/cm² for the bottomlamps.

Once a light intensity is selected, the initial exposure time may bedetermined. A convenient method of monitoring the reaction during thecycle involves fashioning a fine gage thermocouple, positioning itinside the mold cavity, and connecting it to an appropriate dataacquisition system. The preferred thermocouple is Type J, 0.005 inchdiameter, Teflon-insulated wire available from Omega Engineering. Theinsulation is stripped back about 30 to 50 mm and each wire is passedthrough the gasket wall via a fine bore hypodermic needle. The needle isthen removed and the two wires are twisted together to form athermocouple junction inside the inner circumference of the gasket. Theother ends of the leads are attached to a miniature connector which canbe plugged into a permanent thermocouple extension cord leading to thedata acquisition unit after the mold set is filled.

The data acquisition unit may be a Hydra 2625A Data Logger made by JohnFluke Mfg. Company. It is connected to an IBM compatible personalcomputer running Hydra Data Logger software. The computer is configuredto display a trend plot as well as numeric temperature readings on amonitor. The scan interval may be set to any convenient time period anda period of five or ten seconds usually provides good resolution.

The position of the thermocouple junction in the mold cavity may affectits reading and behavior through the cycle. When the junction is locatedbetween the front and back molds, relatively high temperatures may beobserved compared to the temperatures at or near the mold face. Thedistance from the edge of the cavity to the junction may affect bothabsolute temperature readings as well as the shape of the curing cycles'temperature plot. The edges of the lens forming material may begin toincrease in temperature slightly later than other portions of thematerial. Later in the cycle, the lens forming material at the centermay be somewhat ahead of the material at the edge and will tend torespond little to the radiation pulses, whereas the material near theedge may tend to exhibit significant activity. When performingexperiments to develop curing cycles, it is preferred to insert twoprobes into the mold cavity, one near the center and one near the edge.The center probe should be relied upon early in the cycle and the edgeprobe should guide the later stages of the cycle.

Differing rates of reaction among various regions of the lens formingmaterial may be achieved by applying a differential light distributionacross the mold face(s). Tests have been performed where “minus type”light distributions have caused the edge of the lens forming material tobegin reacting before the center of the material. The potentialadvantages of using light distributing filters to cure high masssemi-finished lenses may be offset by nonuniformity of total lighttransmission that tends to occur across large numbers of filters. The UVlight transmission of the PO-4 acrylic plates (Cyro Industries; Plano,Tex.) used over the apertures in the FC-104 curing chamber tends to beconsiderably more consistent than that of silk-screened filter plates.

After the selection and/or configuration of (a) the radiation intensity,(b) the radiation-curable, lens forming material, (c) the mold/gasketset, and (d) the data acquisition system, the optimum initial exposureperiod may be determined. It is useful to expose a sample of lensforming material to continuous radiation to obtain a temperatureprofile. This will provide an identifiable range of elapsed time withinwhich the optimal initial exposure time will fall. Two points ofinterest are the time where the temperature rise in the sample is firstdetected (“T initial” or “Ti”), and the time where the maximumtemperature of the sample is reached (“Tmax”). Also of interest is theactual maximum temperature, an indication of the “heat potential” of thesample under the system conditions (e.g., in the presence of cooling).

As a general rule, the temperature of high mass lenses (i.e., lensesgreater than about 70 grams) should remain under about 200° F. andpreferably between about 150° F. and about 180° F. Higher temperaturesare typically associated with reduced lens yield rates due to crackingand/or premature release. Generally, the lower mass lenses (i.e., lensesno greater than about 45 grains) should be kept under about 150° F. andpreferably between about 110° F. and about 140° F.

The first period may be selected according to the mass of the lensforming material. In an embodiment, the lens forming material has a massof between about 45 grams and about 70 grams and the selected secondtemperature is a temperature between about 150° F. and about 200° F.According to another embodiment, the lens forming material has a mass nogreater than about 45 grams and a second temperature less than about150° F. In yet another embodiment of the invention, the lens formingmaterial has a mass of at least about 70 grams, and a second temperaturebetween about 170° F. and about 190° F.

An experiment may be performed in which the radiation is removed fromthe mold members slightly before one-half of the time between T initialand Tmax. The initial exposure time may be iteratively reduced orincreased according to the results of the above experiment in subsequentexperiments to provide a Tmax in the preferred range. This procedure mayallow the determination of the optimal initial exposure time for anygiven mold/gasket set and light intensity.

A qualitative summary of relationships among system variables related tothe above-described methods is shown in FIG. 22.

After the initial exposure period, a series of irradiation pulse/coolingsteps may be performed to controllably discharge the remainingexothermic potential of the material and thus complete the cure. Thereare at least two approaches to accomplish this second process. The firstinvolves applying a large number of very short pulses and short coolingperiods. The second approach involves applying a fewer number of longerpluses with correspondingly longer cooling periods. Either of these twomethods may produce a good product and many acceptable cycles may existbetween these extremes.

A significant aspect of the invention relates to using pulsedapplication of light to produce a large range (e.g., from −6 to +4diopter) of lenses without requiring refrigerated cooling fluid (e.g.,cooled air). With proper light application, air at ambient may be usedas a cooling fluid, thus significantly reducing system costs.

Some established cycles are detailed in the table below for threesemifinished mold gasket sets: a 6.00 D base curve, a 4.50 D base curve,and a 3.00 D base curve. These cycles have been performed using anFC-104 curing chamber in which cooling air at a temperature of about 56degrees F was directed at the front and back surfaces of a moldassembly. Frosted diffusing window glass was positioned between thesamples and the lamps, with a layer of PO-4 acrylic materialapproximately 1 inch below the glass. A top light intensity was adjustedto 760 microwatts/cm² and a bottom light intensity was adjusted to 950microwatts/cm², as measured at about the plane of the sample. ASpectroline meter DM365N and standard detector stage were used. Anin-mold coating as described in U.S. application Ser. No. 07/931,946 wasused to coat both the front and back molds.

BASE CURVE 6.00 4.50 3.00 Mold Sets Front Mold 5.95 4.45 2.93 Back Mold6.05 6.80 7.80 Gasket −5.00 13 mm 16 mm Resulting Semifinished BlankDiameter 74 mm 76 mm 76 mm Center Thickness 9.0 mm 7.8 mm 7.3 mm EdgeThickness 9.0 mm 11.0 mm 15.0 mm Mass 46 grams 48 grams 57 grams CuringCycle Variables Total Cycle Time 25:00 25:00 35:00 Initial Exposure 4:404:40 4:35 Number of Pulses 4 4 4 Timing (in seconds) and Duration ofPulses @ Elapsed Time From Onset of Initial Exposure Pulse 1 15 @ 10:0015 @ 10:00 15 @ 13:00 Pulse 2 15 @ 15:00 15 @ 15:00 15 @ 21:00 Pulse 330 @ 19:00 30 @ 19:00 20 @ 27:00 Pulse 4 30 @ 22:00 30 @ 22:00 30 @32:00

FIGS. 24, 25, and 26 each show temperature profiles of theabove-detailed cycles for a case where the ultraviolet light exposure iscontinuous and a case where the ultraviolet light delivery is pulsed. InFIGS. 23-26, “Io” denotes the initial intensity of the ultraviolet raysused in a curing cycle. The phrase “Io=760/950” means that the lightintensity was adjusted to initial settings of 760 microwatts/cm² for thetop lamps and 950 microwatts/cm² for the bottom lamps. The “interiortemperature” of FIGS. 23-26 refers to a temperature of the lens formingmaterial as measured by a thermocouple located within the mold cavity.

The following general rules for the design of pulse/cooling cycles maybe employed to allow rapid curing of a lens while inhibiting prematurerelease and/or cracking of the lens. The duration of the pulsespreferably does not result in a temperature that exceeds the maximumtemperature attained in the initial exposure period. The length of thecooling period may be determined by the length of time necessary for theinternal temperature of the lens forming material to return to near thetemperature it had immediately before it received a pulse. Followingthese general rules during routine experimentation may permit propercuring cycles to be established for a broad range of lens formingmaterials, light intensity levels, and cooling conditions.

Preferably light output is measured and controlled by varying the amountof power applied to the lights in response to changes in light output.Specifically, a preferred embodiment of the invention includes a lightsensor mounted near the lights. This light sensor measures the amount oflight, and then a controller increases the power supplied to maintainthe first ultraviolet rays as the intensity of the first ultravioletrays decreases during use, and vice versa. Specifically, the power isvaried by varying the electric frequency supplied to the lights.

A filter is preferably applied to the light sensor so that light wavesother than ultraviolet light impinge less, or not at all, on the lightsensor. In one embodiment, a piece of 365N Glass made by Hoya Optics(Fremont, Calif.) was applied to a light sensor to filter out visiblerays.

One “lamp driver” or light controller was a Mercron Model FX0696-4 andModel FX06120-6 (Mercron, Inc., Dallas, Tex., U.S.A.). These lightcontrollers may be described in U.S. Pat. Nos. 4,717,863 and 4,937,470.

FIG. 13 schematically depicts the light control system described above.The lights 40 in apparatus 10 apply light towards the lens holder 70. Alight sensor 700 is located adjacent the lights 40. Preferably the lightsensor 700 is a photoresistor light sensor (photodiodes or other lightsensors may also be usable in this application). The light sensor 700with a filter 750 is connected to lamp driver 702 via wires 704. Lampdriver 702 sends a current through the light sensor 700 and receives areturn signal from the light sensor 700. The return signal is comparedagainst an adjustable set point, and then the electrical frequency sentto the ultraviolet lights 40 via wires 706 is varied depending on thedifferences between the set point and the signal received from the lightsensor 700. Preferably the light output is maintained within about+/−1.0 percent.

In an embodiment of the invention, a medium pressure mercury vapor lampis used to cure the lens forming material and the lens coating. Thislamp and many conventional light sources used for ultraviolet lightcuring may not be repeatedly turned on and off since a several minutewarm-up period is generally required prior to operation. Mercury vaporlight sources may be idled at a lower power setting between exposureperiods (i.e., second periods), however, the light source will stillgenerate significant heat and consume electricity while at the lowerpower setting.

In an embodiment, a flash lamp emits ultraviolet light pulses to curethe lens forming material. It is believed that a flash lamp wouldprovide a smaller, cooler, less expensive, and more reliable lightsource than other sources. The power supply for a flash lamp tends todraw relatively minimal current while charging its capacitor bank. Theflash lamp discharges the stored energy on a microsecond scale toproduce very high peak intensities from the flash tube itself Thus flashlamps tend to require less power for operation and generate less heatthan other light sources used for ultraviolet light curing. A flash lampmay also be used to cure a lens coating.

In an embodiment, the flash lamp used to direct ultraviolet rays towardat least one of the mold members is a xenon light source. The lenscoating may also be cured using a xenon light source. Referring to FIG.29, xenon light source 980 preferably contains photostrobe 992 having atube 996 and electrodes to allow the transmission of ultraviolet rays.The tube may include borosilicate glass or quartz. A quartz tube willgenerally withstand about 3 to 10 times more power than a hard glasstube. The tube may be in the shape of a ring, U, helix, or it may belinear. The tube may include capacitive trigger electrode 995. Thecapacitive trigger electrode may include a wire, silver strip, orconductive coating located on the exterior of tube 996. The xenon lightsource is preferably adapted to deliver pulses of light for a durationof less than about 1 second, more preferably between about {fraction(1/10)} of a second and about {fraction (1/1000)} of a second, and morepreferably still between about {fraction (1/400)} of a second and{fraction (1/600)} of a second. The xenon source may be adapted todeliver light pulses about every 4 seconds or less. The relatively highintensity of the xenon lamp and short pulse duration may allow rapidcuring of the lens forming composition without imparting significantradiative heat to the composition.

In an embodiment, controller 990 (shown in FIG. 29) controls theintensity and duration of ultraviolet light pulses delivered fromultraviolet light source 980 and the time interval between pulses.Ultraviolet light source 980 may include capacitor 994, which stores theenergy required to deliver the pulses of ultraviolet light. Capacitor994 may be adapted to allow pulses of ultraviolet light to be deliveredas frequently as desired. Temperature monitor 997 may be located at anumber of positions within mold chamber 984. The temperature monitor maymeasure the temperature within the chamber and/or the temperature of airexiting the chamber. The system may be adapted to send a signal tocooler 988 and/or distributor 986 (shown in FIG. 27) to vary the amountand/or temperature of the cooling air. The temperature monitor may alsodetermine the temperature at any of a number of locations proximate themold cavity and send a signal to controller 990 to vary the pulseduration, pulse intensity, or time between pulses as a function of atemperature within mold chamber 984.

In an embodiment, light sensor 999 is used to determine the intensity ofultraviolet light emanating from source 980. The light sensor ispreferably adapted to send a signal to controller 990, which ispreferably adapted to maintain the intensity of the ultraviolet light ata selected level. Filter 998 may be positioned between ultraviolet lightsource 980 and light sensor 999 and is preferably adapted to inhibitvisible rays from contacting light sensor 999, while allowingultraviolet rays to contact the sensor. The filter may include 365 Nglass or any other material adapted to filter visible rays and transmitultraviolet rays.

In an embodiment, a cooling distributor is used to direct air toward thenon-casting face of at least one of the mold members to cool the lensforming composition. The air may be cooled to a temperature of belowambient temperature prior to being directed toward at least one of themold members to cool the composition.

In an embodiment, air at ambient temperature may be used to cool thelens forming composition. Since the xenon flash generally has a durationof much less than about one second, considerably less radiative heattends to be transferred to the lens forming composition compared tocuring methods employing other ultraviolet sources. Thus, the reducedheat imparted to the lens forming composition may allow for air atambient temperature to remove sufficient heat of exotherm tosubstantially inhibit premature release and/or cracking of the lens.

In an embodiment, the xenon source is used to direct first ultravioletrays toward the first and second mold members to the point that atemperature increase is measured and/or the lens forming compositionbegins to or forms a gel. It is preferred that the gel is formed withless than 15 pulses of radiation, and more preferably with less thanabout 5 pulses. It is preferred that the gel is formed before the totaltime to which the composition has been exposed to the pulses exceedsabout {fraction (1/10)} or {fraction (1/100)} of a second.

In an embodiment, a reflecting device is employed in conjunction withthe xenon light source. The reflecting device is positioned behind theflash source and preferably allows an even distribution of ultravioletrays from the center of the composition to the edge of the composition.

In an embodiment, a xenon light flash lamp is used to apply a pluralityof ultraviolet light pulses to the lens forming composition to cure itto an eyeglass lens in a time period of less than 30 minutes, or morepreferably, less than 20 or 15 minutes.

The use of a xenon light source also may allow the formation of lensesover a wider range of diopters. Higher power lenses exhibit greatestthinnest to thickest region ratios, meaning that more shrinkage-inducedstress is created, causing greater mold flexure and thus increasedtendency for premature release. Higher power lenses also possess thickerregions. Portions of lens forming material within these thicker regionsmay receive less light than lens forming material within regions closerto the mold surfaces. Continuous irradiation lens forming techniquestypically require the use of relatively low light intensities to controlthe heat generated during curing. The relatively low light intensitiesused tend to result in a long, slow gelation period. Optical distortionstend to be created when one portion of the lens is cured at a differentrate than another portion. Methods characterized by non-uniform curingare typically poorly suited for the production of relatively high powerlenses, since the deeper regions (e.g., regions within a thick portionof a lens) tend to gel at a slower rate than regions closer to the moldsurfaces.

The relatively high intensity attainable with the xenon source may allowdeeper penetration into, and/or saturation of, the lens formingmaterial, thereby allowing uniform curing of thicker lenses than inconventional radiation-initiated curing. More uniform gelation tends tooccur where the lens forming material is dosed with a high intensitypulse of ultraviolet light and then subjected to decreased UV light ordarkness as the reaction proceeds without activating radiation. Lenseshaving a diopter of between about +5.0 and about −6.0 and greater may becured. It is believed that light distribution across the sample is lesscritical when curing and especially when gelation is induced withrelatively high intensity light. The lens forming material may becapable of absorbing an amount of energy per time that is below thatdelivered during a relatively high intensity pulse. The lens formingmaterial may be “oversaturated” with respect to the light delivered viaa high intensity flash source. In an embodiment, the xenon source isused to cure a lens having a diopter between about −4.0 and about −6.0.In an embodiment, the xenon source is used to cure a lens having adiopter between about +2.0 and about +4.0.

In an embodiment, more than one xenon light source is usedsimultaneously to apply lo ultraviolet pulses to the lens formingcomposition. Such an embodiment is shown in FIG. 28. Xenon light sources980 a and 980 b may be positioned around mold chamber 985 so that pulsesmay be directed toward the front face of a lens and the back face of alens substantially simultaneously. Mold chamber 985 is preferablyadapted to hold a mold in a vertical position such that pulses fromxenon source 980 a may be applied to the face of a first mold member,while pulses from source 980 b may be applied to the face of a secondmold member. In an embodiment, xenon source 980 b applies ultravioletlight pulses to a back surface of a lens more frequently than xenonsource 980 a applies ultraviolet light pulses to a front surface of alens. Xenon sources 980 a and 980 b may be configured such that onesource applies light to mold chamber 984 from a position above thechamber while the other xenon source applies light to the mold chamberfrom a position below the chamber.

In an embodiment, a xenon light source and a relatively low intensity(e.g., fluorescent) light source are used to simultaneously applyultraviolet light to a mold chamber. As illustrated in FIG. 27, xenonsource 980 may apply ultraviolet light to one side of mold chamber 984while low intensity fluorescent source 982 applies ultraviolet light toanother side of the mold chamber. Fluorescent source 982 may include acompact fluorescent “light bucket” or a diffused fluorescent lamp. Thefluorescent light source may deliver continuous or substantially pulsedultraviolet rays as the xenon source delivers ultraviolet pulses. Thefluorescent source may deliver continuous ultraviolet rays having arelatively low intensity of less than about 0.1 watts/cm².

Methods of the present invention allow curing of high-mass semi-finishedlens blanks from the same material used to cure cast-to-finish lenses.Both are considered to be “eyeglass lenses” for the purposes of thispatent. These methods may also be used to cure a variety of other lensforming materials. Methods of the present invention have beensuccessfully used to make cast-to-finish lenses in addition tosemi-finished lenses.

PULSE METHOD EXAMPLE 1 USE OF A MEDIUM PRESSURE VAPOR LAMP

An eyeglass lens was successfully cured with ultraviolet light utilizinga medium pressure mercury vapor lamp as a source of activating radiation(i.e., the UVEXS Model 912 previously described herein). The curingchamber included a six inch medium pressure vapor lamp operating at apower level of approximately 250 watts per inch and a defocused dichroicreflector that is highly UV reflective. A high percentage of infraredradiation was passed through the body of the reflector so that it wouldnot be directed toward the material to be cured. The curing chamberfurther included a conveyer mechanism for transporting the sampleunderneath the lamp. With this curing chamber, the transport mechanismwas set up so that a carriage would move the sample from the front ofthe chamber to the rear such that the sample would move completelythrough an irradiation zone under the lamp. The sample would then betransported through the zone again to the front of the chamber. In thismanner the sample was provided with two distinct exposures per cycle.One pass, as defined hereinafter, consists of two of these distinctexposures. One pass provided a dosage of approximately 275 millijoulesmeasured at the plane of the sample using an International Light IL 1400radiometer equipped with a XRL 340 B detector.

A lens cavity was created using the same molds lens forming composition,and gasket of Pulsed Method Example 2 below. The reaction cellcontaining the lens forming material was placed on a supporting stagesuch that the plane of the edges of the convex mold were at a distanceof approximately 75 mm from the plane of the lamp. The lens cavity wasthen exposed to a series of UV doses consisting of two passes directedto the back surface of the mold followed immediately by one passdirected to the front surface of the mold. Subsequent to these firstexposures, the reaction cell was allowed to cool for 5 minutes in theabsence of any activating radiation in an FC-104 chamber as described inPulsed Method Example 1 at an air temperature of 74.6 degrees F and atan air flow rate of approximately 15 to 25 scf per minute to the backsurface and 15 to 25 scf to the front surface of the cell. The lenscavity was then dosed with one pass to the front mold surface andreturned to the cooling chamber for 6 minutes. Then the back surface wasexposed in one pass and then was cooled for 2 minutes. Next, the frontsurface was exposed in two passes and then cooled for 3.5 minutes. Thefront surface and the back surface were then each exposed to two passes,and the gasket was removed to expose the edges of the lens. A strip ofpolyethylene film impregnated with photoinitiator was then wrappedaround the edge of the lens and the front and back surfaces were exposedto another 3 passes each. The back surface of the cell was then placedon the conductive thermal in-mold postcure device using a “bean-bag”container filled with glass beads on a hot plate at about 340° F.described previously (see conductive heating example 1) for a timeperiod of 13 minutes, after which the glass molds were removed from thefinished lens. The finished lens exhibited a distance focusing power of−6.09 diopters, had excellent optics, was aberration-free, was 74 mm indiameter, and had a center thickness of 1.6 mm. During the coolingsteps, a small surface probe thermistor was positioned against theoutside of the gasket wall to monitor the reaction. The results aresummarized below.

Approx. Elapsed Time Gasket Wall UV Dose After UV Dose (min) Temperature(° F.) 2 passes to back 0 Not recorded surface and 1 pass to frontsurface 1 80.5 2 79.7 3 79.0 4 77.1 5 76.2 1 pass to front surface 0 Notrecorded 1 83.4 2 86.5 3 84.6 4 Not recorded 5 81.4 6 79.5 1 pass toback surface 0 Not recorded 1 79.3 2 79.0 2 passes to front surface 0Not recorded 1 78.4 2 77.8 3 77.0   3.5 76.7

PULSE METHOD EXAMPLE 2 USE OF A SINGLE XENON FLASH LAMP

An eyeglass lens was successfully cured with ultraviolet light utilizinga xenon flash lamp as a source of activating radiation. The flash lampused was an Ultra 1800 White Lightning photographic strobe, commerciallyavailable from Paul C. Buff Incorporated of Nashville, Tenn. This lampwas modified by replacing the standard borosilicate flash tubes withquartz flash tubes. A quartz flash tube is preferred because some of theultraviolet light generated by the arc inside the tube tends to beabsorbed by borosilicate glass. The strobe possessed two semicircularflash tubes that trigger simultaneously and are positioned to form aring approximately 73 millimeters in diameter. The hole in the reflectorbehind the lamps, which normally contains a modeling lamp forphotographic purposes, was covered with a flat piece of highly-polishedultraviolet reflective material, which is commercially available underthe trade name of Alzac from Ultra Violet Process Supply of Chicago,Ill. The power selector switch was set to fill power. The ultravioletenergy generated from one flash was measured using an InternationalLight IL 1700 Research Radiometer available from International Light,Incorporated of Newburyport, Massachusetts. The detector head was anInternational Light XRL 340 B, which is sensitive to radiation in the326 nm to 401 nm region. The window of the detector head was positionedapproximately 35 mm from the plane of the flash tubes and wasapproximately centered within the ring formed by the tubes. The resultsshowed the power of one flash to be about 940 microwatts.

A mold cavity was created by placing two round 80 mm diameter crownglass molds into a silicone rubber ring or gasket, which possessed araised lip around its inner circumference. The edges of the glass moldsrested upon the raised lip to form a sealed cavity in the shape of thelens to be created. The inner circumference of the raised lipcorresponded to the edge of the finished lens. The concave surface ofthe first mold corresponded to the front surface of the finished lensand the convex surface of the second mold corresponded to the backsurface of the finished lens. The height of the raised lip of the rubberring into which the two glass molds are inserted controls the spacingbetween the two glass molds, thereby controlling the thickness of thefinished lens. By selecting proper gaskets and first and second moldsthat possess various radii of curvature, lens cavities can be created toproduce lenses of various powers.

A lens cavity was created by placing a concave glass mold with a radiusof curvature of 407.20 mm and a convex glass mold with a radius ofcurvature of 65.26 mm into a gasket which provided spacing between themolds of 1.8 mm measured at the center of the cavity. Approximately 32grams of a lens forming monomer was charged into the cavity. The lensforming material used for this test was OMB-91 lens monomer. Thereaction cell containing the lens forming material was placedhorizontally on a supporting stage such that the plane of the edges ofthe convex mold were at a distance of approximately 30 mm from the planeof the flash tubes and the cell was approximately centered under thelight source.

The back surface of the lens cavity was then exposed to a first seriesof 5 flashes, with an interval of approximately 4 seconds in betweeneach flash. The cell was then turned over and the front surface wasexposed to another 4 flashes with intervals of about 4 seconds inbetween each flash. It is preferable to apply the first set of flashesto the back surface to start to cure the material so that any airbubbles in the liquid monomer will not migrate from the edge of thecavity to the center of the optical zone of the lens. Subsequent tothese first nine flashes, the reaction cell was allowed to cool for fiveminutes in the absence of any activating radiation in theabove-described FC-104 chamber. To cool the reaction cell, air at atemperature of 71.4 degrees F and at a flow rate of approximately 15 to25 scf per minute was applied to the back surface and air at atemperature of 71.4 degrees F and at a flow rate of approximately 15 to25 scf per minute was applied to the front surface of the cell. The backsurface of the lens cavity was then dosed with one more flash andreturned to the cooling chamber for four minutes.

Next, the cell was exposed to one flash on the front surface and cooledin the cooling chamber for seven minutes. Then the cell was exposed toone flash on the front surface and one flash on the back surface andcooled for three minutes. Next, the cell was exposed to two flashes onthe front surface and two flashes on the back surface and cooled forfour and a half minutes. The cell was then exposed to five flashes eachto the back surface and front surface, and the gasket was removed toexpose the edges of the lens. A strip of polyethylene film impregnatedwith photoinitiator (Irgacure 184) was then wrapped around the edge ofthe lens, and the cell was exposed to another five flashes to the frontsurface and fifteen flashes to the back surface. The back surface of thecell was then placed on the conductive thermal in-mold postcure device(i.e., “bean bags” filled with glass beads sitting on a hot plate atapprox. 340° F.) as described previously (see conductive heating exampleabove) for a time period of 13 minutes, after which the glass molds wereremoved from the finished lens. The finished lens exhibited a distancefocusing power of −6.16 diopters and a +2.55 bifocal add power, hadexcellent optics, was aberration-free, was 74 mm in diameter, and had acenter of thickness of 1.7 mm. During the cooling steps, a small surfaceprobe thermistor was positioned against the outside of the gasket wallto monitor the reaction. The results are summarized below.

Elapsed Time From Gasket Wall Dose Dose (min) Temperature (F.) 5 flashesto back surface and 4 0 Not recorded flashes to front surface 1 Notrecorded 2 78.4 3 77.9 4 76.9 5 75.9 1 flash to back surface 0 Notrecorded 1 76.8 2 77.8 3 78   4 77.8 1 flash to front surface 0 Notrecorded 1 79.4 2 81.2 3 81.1 4 79.7 5 78.7 6 77.5 7 77.4 1 flash tofront surface and 1 0 Not recorded flash to back surface 1 78.8 2 78.8 378.0 2 flashes to front surface and 2 0 Not recorded flashes to backsurface 1 80.2 2 79.8 3 78.3 4 76.7   4.5 76.3

Further modifications and alternative embodiments of various aspects ofthe invention will be apparent to those skilled in the art in view ofthis description. Accordingly, this description is to be construed asillustrative only and is for the purpose of teaching those skilled inthe art the general manner of carrying out the invention. It is to beunderstood that the forms of the invention shown and described hereinare to be taken as the presently preferred embodiments. Elements andmaterials may be substituted for those illustrated and described herein,parts and processes may be reversed, and certain features of theinvention may be utilized independently, all as would be apparent to oneskilled in the art after having the benefit of this description of theinvention. Changes may be made in the elements and compositionsdescribed herein or in the features or in the sequence of features ofthe methods described herein without departing from the spirit and scopeof the invention as described in the following claims.

What is claimed is:
 1. An eyeglass lens made by the method comprising:placing a liquid polymerizable lens forming composition in a mold cavitydefined by at least a first mold member and a second mold member;wherein the liquid polymerizable lens forming composition comprises: aphotoinitiator; an aromatic containing bis(allyl carbonate)-functionalmonomer; and a polyethylenic-functional monomer containing at least twoethylenically unsaturated groups selected from acrylyl and methacrylyl;directing first ultraviolet rays toward at least one of the mold membersto cure the lens forming composition so that it forms a lens with a backface, edges, and a front face; applying a mold member of the mold cavityto a substantially solid conductive heat source; and conductivelyapplying heat to a face of the lens by (a) conductively transferringheat to a face of a mold member from the conductive heat source, and (b)conductively transferring heat through such mold member to the face ofthe lens.
 2. The eyeglass lens of claim 1 wherein the mold cavityfurther comprises a gasket, and wherein the method further comprisesremoving the gasket from the mold cavity after the lens is formed butbefore conductively transferring heat to the face of the mold member. 3.The eyeglass lens of claim 1 wherein the method further comprisestreating the edges of the lens to cure or remove incompletely cured lensforming material before conductively applying heat.
 4. The eyeglass lensof claim 1 wherein heat is substantially uniformly applied to the faceof the mold member.
 5. The eyeglass lens of claim 1 wherein the heatsource comprises a substantially concave element configured tosubstantially conform to a substantially convex face of a mold member.6. The eyeglass lens of claim 1 wherein the heat source comprises asubstantially convex element configured to substantially conform to asubstantially concave face of a mold member.
 7. The eyeglass lens ofclaim 1, wherein the method further comprises using a heat distributorbetween the mold member and the heat source.
 8. The eyeglass lens ofclaim 1, wherein the method further comprises using a heat distributorbetween the mold member and the heat source to partially insulate themold member from the heat source, and such that heat is graduallytransferred from the heat source to the mold member.
 9. The eyeglasslens of claim 1, wherein the method further comprises thermostaticallycontrolling the temperature of the heat source.
 10. The eyeglass lens ofclaim 1, wherein the method further comprises using a flexible heatdistributor between the mold member and the heat source.
 11. Theeyeglass lens of claim 1, wherein the method further comprises using aflexible heat distributor between the mold member and the heat source,and wherein the heat distributor comprises a container containingparticles.
 12. The eyeglass lens of claim 1, wherein the method furthercomprises using a flexible heat distributor between the mold member andthe heat source, and wherein the heat distributor comprises a containercontaining particles of a metal or ceramic material.
 13. The eyeglasslens of claim 1, wherein the method further comprises using a flexibleheat distributor between the mold member and the heat source, andwherein the method further comprises shaping the flexible heatdistributor to substantially conform to a face of a mold member.
 14. Theeyeglass lens of claim 1, wherein heat is only conductively applied toone outside face of one mold member.
 15. The eyeglass lens of claim 1wherein heat is conductively applied through a mold member to the backface of the lens, thereby enhancing cross-linking of the lens formingmaterial proximate to the surface of the back face of the lens.
 16. Theeyeglass lens of claim 1 wherein heat is conductively applied through amold member to the back face of the lens, thereby increasing thetintability of the back surface of the lens.
 17. The eyeglass lens ofclaim 1, wherein the method further comprises tinting the lens.
 18. Theeyeglass lens of claim 1, wherein the method further comprises tintingthe lens by immersing the lens in a dye solution without substantiallyagitating the dye solution.
 19. A plastic eyeglass lens made by themethod comprising: placing a liquid polymerizable lens formingcomposition in a mold cavity defined by at least a gasket, a first moldmember, and a second mold member; wherein the liquid polymerizable lensforming composition comprises: a photoinitiator; an aromatic containingbis(allyl carbonate)-functional monomer; and a polyethylenic-functionalmonomer containing at least two ethylenically unsaturated groupsselected from acrylyl and methacrylyl; directing first ultraviolet raystoward at least one of the mold members to cure the lens formingcomposition so that it forms a lens with a back face, edges, and a frontface; shaping a flexible member such that it substantially conforms to aface of a mold member; applying a mold member of the mold cavity to theflexible member, the flexible member being on top of a conductive heatsource; conductively applying heat to a face of the lens by (a)conductively applying heat to a face of a mold member from theconductive heat source, and (b) conductively transferring heat throughsuch mold member to the lens.
 20. The eyeglass lens of claim 19 whereinthe flexible member is coupled to the conductive heat source.
 21. Theeyeglass lens of claim 19 wherein the mold cavity further comprises agasket, and further comprising removing the gasket from the mold cavityafter the lens is formed but before conductively transferring heat tothe face of the mold member.
 22. The eyeglass lens of claim 19, whereinthe method further comprises treating the edges of the lens to cure orremove incompletely cured lens-forming material before conductivelyapplying heat.
 23. The eyeglass lens of claim 19 wherein heat issubstantially uniformly applied to the face of the mold member.
 24. Theeyeglass lens of claim 19 wherein the heat source comprises asubstantially concave element configured to substantially conform to asubstantially convex face of a mold member.
 25. The eyeglass lens ofclaim 19 wherein the heat source comprises a substantially convexelement configured to substantially conform to a substantially concaveface of a mold member.
 26. The eyeglass lens of claim 19 wherein theflexible member acts as a heat distributor between the mold member andthe heat source.
 27. The eyeglass lens of claim 19 wherein the flexiblemember acts as a heat distributor between the mold member and the heatsource to partially insulate the mold member from the heat source, andsuch that heat is gradually transferred from the heat source to the moldmember.
 28. The eyeglass lens of claim 19, wherein the method furthercomprises thermostatically controlling the temperature of the heatsource.
 29. The eyeglass lens of claim 19 wherein the flexible membercomprises a container containing particles.
 30. The eyeglass lens ofclaim 19 wherein the flexible member comprises a container containingparticles of a metal or ceramic material.
 31. The eyeglass lens of claim1 wherein the liquid polymerizable lens forming composition comprises atleast 25% by weight of the polyethylenic-functional monomer containingat least two ethylenically unsaturated groups selected from acrylyl andmethacrylyl.
 32. The eyeglass lens of claim 19 wherein the liquidpolymerizable lens forming composition comprises at least 25% by weightof the polyethylenic-functional monomer containing at least twoethylenically unsaturated groups selected from acrylyl and methacrylyl.33. The plastic eyeglass lens of claim 1 wherein the liquidpolymerizable lens forming composition comprises less than about 30percent by weight of an aromatic containing bis(allylcarbonate)-functional monomer.
 34. The plastic eyeglass lens of claim 19wherein the liquid polymerizable lens forming composition comprises lessthan about 30 percent by weight of an aromatic containing bis(allylcarbonate)-functional monomer.